L 


A. 


A  TEXT-BOOK 


OF 


VOLUMETRIC    ANALYSIS 

WITH    SPECIAL    REFERENCE   TO 

THE  VOLUMETRIC   PROCESSES   OF  THE 

PHARMACOPCEIA  OF  THE  UNITED  STATES. 


DESIGNED  FOR  THE  USE  OF  PHARMACISTS 
AND  PHARMACEUTICAL  STUDENTS. 


BY 

HENRY  W.  SCHIMPF,  Pn.G. 

Professor  of  Inorganic  Chemistry  in  the  Brooklyn  College  of  Pharmacy  ;  Food 

Inspector  of  the  Department  of  Health  of  the  City  of  Brooklyn  ;  Member 

of  the  American  Association  for  the  Advancement  of  Science  ;  of  the 

American   Pharmaceutical  Association  ;    of  the    Kings   County 

Pharmaceutical  Society  ;    of  the  Brooklyn  Institute  ;  of  the 

German  Apothecaries  Society  of  the  City  of  Neiu  York; 

Honorary    Member    of  the   Alumni  Association   of 

the  Brooklyn    College  of  Pharmacy,  etc.,  etc. 


SECOND    EDITION. 

FIRST  THOUSAND. 

InriTiRsirr] 

& 

NEW    YORK  : 

>HN    WILEY   &    SONS. 

LONDON:    CHAPMAN    &    HALL,    LIMITED. 
1895. 


Copyright,  1894, 

HY 

HENRY  W.  SCHIMPK. 


ROBERT   DRUMMOND,   ELECTROTYPER   ANP   PRINTER,    NEW  YORK. 


triU7BRSIT7 


PREFACE. 


THIS  book  is  designed  for  the  use  of  pharmacists, 
and  especially  as  a  text-book  for  students  in  pharmacy. 

In  the  first  portion  of  the  book  the  author  has  at- 
tempted, in  explaining  the  principles  of  volumetric 
analysis,  to  combine  thoroughness  with  simplicity  of 
expression. 

The  United  States  Pharmacopoeia  has  been  taken  as 
the  basis  of  the  work,  and  the  volumetric  processes 
therein  given  are  followed  throughout,  each  step  being 
carefully  explained,  and  chemical  equations  inserted, 
wherever  deemed  necessary. 

The  author  has  also  added  descriptions  of  processes 
not  given  in  the  Pharmacopoeia,  but  which  are  worthy 
of  consideration. 

In  teaching  volumetric  analysis  to  students  in  phar- 
macy the  author  discovered  the  necessity  for  a  work 
especially  designed  for  this  class  of  students. 

Moreover,  the  requirements  of  the  new  edition  of  the 
United  States  Pharmacopoeia,  in  which  many  volumet- 
ric processes  are  given,  necessitate  on  the  part  of  the 
careful  pharmacist  a  knowledge  of  this  branch  of  ana- 
lytical chemistry;  and  no  work  that  has  as  yet  fallen 
into  the  hands  of  the  author  has  seemed  to  be  exactly 
suited  to  the  needs  of  the  practical  pharmacist.  Con- 
sequently the  necessity  for  a  book  based  upon  the 
Pharmacopoeia  and  free  from  technicality  is  apparent. 

iii 


IV  PREFACE. 

The  latter  portion  of  the  book  is  devoted  to  descrip- 
tions of  such  special  analytical  processes  as  the  phar- 
macist may  be  called  upon  to  use,  and  such  as  are 
taught  in  the  pharmaceutical  colleges. 

The  author  has  selected  such  processes  as  can  be 
easily  and  quickly  executed,  and  has  given  the  gravi- 
metric only  where  volumetric  processes  cannot  be 
employed. 

In  the  subject-matter  of  the  book  little  originality  is 
claimed,  but  the  author  has  used  his  own  judgment  in 
its  selection  and  arrangement. 

He  has  endeavored  in  the  text  to  give  credit  wher- 
ever it  was  due,  and  especially  acknowledges  his  indebt- 
edness to  the  United  States  Pharmacopoeia  ;  Button's 
Volumetric  Analysis  ;  Hartley's,  Simon's,  and  Attfield's 
text-books  ;  Blythe's  Food  Analysis  ;  Prescott's  Organic 
Analysis ;  Muter's  Analytical  Chemistry  (American 
edition}  ;  Lefmann  and  Beam's  Milk  and  Water  Analy- 
sis ;  and  Witthaus'  and  Holland's  Urine  Analysis. 

He  wishes  to  express  his  thanks  to  Dr.  J.  F.  Gold- 
ing  for  the  valued  assistance  he  has  rendered  during 
the  preparation  of  the  book.  He  is  also  indebted 
to  Richards  &  Co.,  of  41  Barclay  Street,  N.  Y.  City, 
manufacturers  of  chemical  apparatus,  from  whom  sev- 
eral of  the  cuts  were  borrowed. 

The  author  submits  this  work  to  the  consideration 
of  pharmacists,  trusting  its  reception  will  be  at  least 
commensurate  with  the  labor  expended  in  its  prepa- 
ration. 

HENRY  W.  SCHIMPF. 

365  FRANKLIN  AVE.,  BROOKLYN,  N.  Y. 


TABLE  OF  CONTENTS. 


PAGE 

TABLE  OF  THE  ELEMENTS  AND  THEIR  ATOMIC  WEIGHTS  .        .  xvii 
ABBREVIATIONS  AND  SIGNS  .  „  xviii 


PART   I, 

CHAPTER  I. 

Quantitative  Analysis .  I 

The  Gravimetric  Method I 

The  Volumetric  Method e        .  I 

CHAPTER  II. 

Standard  and  Normal  Solutions    .•<,...,  4 

Normal  Solutions 4 

Standard  Solutions 4 

"Standardized,"  "Set,"  or  "Titrated "Solutions         ...  4 

Decinormal  Solutions «,         .         .         .  8 

Centinormal        '*          .         ....        0         ...  8 

Semi-normal       "          .  '     * r 9 

Double-normal   " 9 

Empirical                          •  9 

To  "Titrate"         .                                    9 

Residual  Titration         . .9 

CHAPTER  III. 

Indicator  defined 10 

Litmus  Tincture .10 

Phenolphthalein  T.  S.                    , 10 

V 


vi  TABLE  OF   CONTENTS. 

PAGE 

Methyl-Orange  T.  S n 

Rosolic  Acid  T.  S ,     n 

Turmeric  T.  S n 

Cochineal  T.  S n 

Eosin  T.  S u 

Brazil-wood  T.  S n 

Fluorescein  T.  S.  . n 

Potassium  Chromate  T.  S.     „         .         .         ,        .         .         .         .11 
Potassium  Ferricyanide  T.  S.        .        .        .        .        .        .        .11 

CHAPTER  IV. 
GENERAL  PRINCIPLES       .        .        .        .12 

CHAPTER  V. 

WEIGHTS  AND  MEASURES  USED  IN  VOLUMETRIC  ANALYSIS.  15 

Graduation  of  Instruments 16 

Table  showing  Expansion  and  Contraction  of  Liquids  at  Different 

Temperatures 16 

CHAPTER  VI 

APPARATUS  USED  IN  VOLUMETRIC  ANALYSES    .        .17 

The  Burette .        .        .17 

Mohr's  Burette 17 

Glass-cock  Burette 17 

Oblique-cock  Burette 18 

Mohr's  Foot  Burette  with  Rubber  Ball 19 

GayLussac's  Burette      .         .         .         .         „         .         0         .         .19 

Bink's  Burette .         .         .19 

Bead  Stop      ...........     2O 

Burette  Stand 25 

Measuring-flask :         ....     20 

Test-mixer     ...» 21 

Pipettes 21 

Single-volume  Pipettes          .00 21 

Graduated  Pipettes        .         .         0 21 

Bead  Pipette 22 

Nipple  Pipette 22 

Burette  attached  to  Reservoir       ..•»...     24 


TABLE  OF  CONTENTS.  Vll 

CHAPTER  VIL 

PAGE 

USE  OF  APPARATUS        .        .        .        .27 

Cleaning  the  Instruments .         b     27 

Filling  the  Burette 27 

Reading  the  Instruments  .......     28 

Half-blackened  Card  .     29 

Erdman's  Float .     30 

CHAPTER  VIII. 

CALCULATING  RESULTS     .        .        ,        .31 

Rules  for  finding  Percentage 31 

Factors  or  Coefficients  .         .         .         .         .         .         .         -33 

Table  of  Approximate  Normal  Factors  for  Alkalies  and  Acids     .     35 

CHAPTER   IX. 

ANALYSES  BY  NEUTRALIZATION      .  '36 

Alkalimetry    .         .,        .         ...         .         .         .      "   .         .36 

Preparation  of  Standard  Oxalic-acid  Solutions      .         .         .         .39 

Preparation     of    Standard     Sulphuric    and     Hydrochloric   Acid 

Solutions        ..         ...         .         .         .         .         .       40,  41 

Estimation  of  Alkaline  Hydroxides         »         *        .         .         .         .43 

Potassa       j  ...        ..        ^      .".,       ... .      * 43 

Liquor  Potassa 44 

Soda 0 45 

Liquor  Soda 45 

Aqua  Ammonia  „         „         .         .         .     46 

Fortior .46 

Spirit  of  Ammonia  r  ..  " .  ...  .  0  .  .47 
Estimation  of  Alkaline  Carbonates  ,  *•  .  .  .  .  .  47 
Potassium  Carbonate  .  '  *.  «...  .'  .  .  .  .48 

Potassium  Bicarbonate          •«      •  •% 49 

Sodium  Carbonate         ...        .  ;...        .    >:^  *.';!  .T  .  •  •     .         .     49 

Sodium  Bicarbonate      .         .         »         .         •        .         .         .         .50 

Ammonium  Carbonate  .         „        *         .         .         .         .         .51 

Lithium  Carbonate        ...         .         ,.         .         .         .         .         .51 

Borax     .......  ....     54 

Estimation  of  Organic  Salts  of  the  Alkalies  ,         .         .         .     54 

Potassium  Tartrate        .         .  .  «         •         .     55 

Potassium  and  Sodium  Tartrate  .  v         .         .         .57 


viii  TABLE   OF  CONTENTS. 

PAGE 

Potassium  Bitartrate  ...,„...  58 

Lithium  Citrate  ....  o  ....  59 

Potassium  Citrate  ....  0  ....  60 

Potassium  Acetate  .  .  .  .  0  •  .  •  .  .61 

Sodium  Acetate 62 

Lithium  Benzoate  ,         ........     63 

Sodium  Benzoate  ......  ...  64 

Lithium  Salicylate  . .  66 

Sodium  Salicylate 67 

Table  showing  Normal  Factors  for  the  Organic  Salts  of  the 

Alkalies 68 

Acidimetry     ...........     68 

Special  Vessels  for  Preserving  Alkali  Solutions     .         .         .         .69 

Preparation  of  Normal  Alkali  Solutions  .  .  .  .  .69 

Acetic  Acid 73 

"  Diluted 74 

"  Glacial 76 

Vinegar  ' 74 

Free  Mineral  Acids  in  Vinegar  .  75 

Citric  Acid 76 

Lime  and  Lemon  Juice .  77 

Hydrobromic  Acid «...  77 

Hydrochloric  Acid ...  78 

Hypophosphorous  Acid  . 79 

Lactic  Acid o  .  .  .  .  80 

Nitric  Acid  .  81 

«•  "  Diluted  .  .  .  .  ' 82 

Phosphoric  Acid .  82 

"  Diluted  .  c  o 82 

"  "     (Stolba's  Method)       ......     82 

Sulphuric  Acid .  86 

"          "     Aromatic 87 

"  "  Diluted 87 

Tartaric  Acid 87 

Table  showing  Normal  Factors,  etc.,  for  the  Acids  .  .  .88 

Estimation  of  Alkaline  Earths .88 

Preparation  of  Normal  Sodium  Carbonate  V.  S,  .  .  .  .89 

Liquor  Calcis .90 

Calcium  Carbonate 91 

"  Bromide  ..,.<>....  92 


TABLE  OF  CONTENTS.  IX 

PAGE 

Calcium  Chloride  .........     93 

Barium  Chloride 93 

"        Nitrate 93 

Strontium  Lactate          ..  ......94 

CHAPTER  X. 

ANALYSIS  BY  PRECIPITATION  .        ,96 

Estimation  of  Haloid  Sails     ........  97 

Preparation  of  Decinormal  Silver  Nitrate  V.  S.    .         .         .         •  97 

Ammonium  Bromide .  99 

Lithium  Bromide 101 

Potassium  Bromide       .        , 101 

Sodium  Bromide 102 

Strontium  Bromide 103 

Calcium  Bromide 103 

Zinc  Bromide 104 

Potassium  Iodide  .                  105 

"             "      Personnel  Method 106 

Sodium  Iodide 107 

Strontium  Iodide  ...;..                                    .  108 

Zinc  Iodide 108 

Ammonium  Chloride ,  109 

Potassium  Chloride 109 

Sodium  Chloride .no 

Zinc  Chloride         .         .         .         .         .         .         .        .         .         .no 

Syrup  of  Hydriodic  Acid in 

«      4.  Ferrous  Iodide .         .112 

«      «  Ferrous  Bromide 117 

Saccharated  Ferrous  Iodide  .         *         *        *        .         .         .         .  116 
Preparation  and  Use  of  Standard  Potassium  Sulphocyanate  V.  S. 

(Volhard's  Solution) .113 

Hydrocyanic  Acid 117 

Potassium  Cyanide        .         .        .         .                  .         .         .         .  120 

Silver  Nitrate 121 

"       Fused 123 

"            "       Diluted  .                  123 

"      Oxide 124 

Liquor  Plumbi  Subacetatis    ....         e         ...  124 

T$ble  showing  Factors  of  Substances  estimated  by  Precipitation.  125 


X  TABLE  OF  CONTENTS. 

CHAPTER  XL 

PAGE 
OXIDIMETRY 127 

Estimation  of  Ferrous  Salts  .         .         .         .         .         .         .         .126 

Preparation  of  Standard  Solution  of  iKMnO^  and  K-^Cr^Oi  .   129 

Estimation  of  Ferrous  Salts  by  IC•iCr^O^ 133 

Saccharated  Ferrous  Carbonate     .         .        ,         .         .         0         .138 

Ferrous  Sulphate ,  140 

Estimation  of  Ferrous  Salts  by  zICMnO*        .         .         .         .         .141 

Ferrum  Reductum 143 

Ferrous  Sulphate  ,  .   145 

Estimation  of  other  Oxidizable  Substances  .         .         .         .         .145 

Hypophosphorous  Acid 146 

Calcium  Hypophosphite 148 

Ferric  Hypophosphite  .         .         . 149 

Potassium  Hypophosphite 150 

Sodium  Hypophosphite         ........   151 

Hydrogen  Peroxide       .  152 

Barium  Dioxide     . .157 

Oxalic  Acid .158 

Table  of  Substances  which  may  be  Estimated  by  Oxidation         .  160 

CHAPTER   XII. 

ANALYSIS  BY  INDIRECT  OXIDATION          ,        .  161 
Preparation  of  Standard  Solution  of  Iodine   .         .     -;..',         .162 

Arsenous  Acid       .         .         .         .        .         .        «         ••:/.«•         •  *63 

Liquor  Acidi  Arsenosi,  U.  S.  P.  .         .        .;     .  f         .        .         .  164 

Liquor  Potassa  Arsenitis,  U.  S.  P 165 

Sulphurous  Acid   ......         0         ...  165 

Sodium  Sulphite    .                                               166 

Potassium  Sulphite                 .                                    «...  167 

Sodium  Bisulphite         ...                  .                                    .  168 

Sodium  Thiosulphate    ...                  168 

Antimony  and  Potassium  Tartrate 169 

Table  of  Substances  which  may  be  Estimated  by  Iodine  .         0         .171 

CHAPTER  XIII. 

ESTIMATION  OF  SUBSTANCES  READILY  REDUCED  .  172 
Preparation  of  Standard  Solution  of  Sodium  Thiosulphate  .  .173 
Estimation  of  Free  Iodine 175 


TABLE  OF   CONTENTS.  xi 

PAGE 

Liquor  lodi  Compositus 176 

Tincture  of  Iodine 177 

Aqua  Chlori .         .         .         , 177 

Calx  Chlorata ...  178 

The  Arsenous  Acid  Process 180 

Preparation  of  —  A  rsenous-acid  Solution       .         .         .         .         .  1 8 1 
J  10 

Liquor  Sodae  Chloratae 181 

Estimation  of  Ferric  Salts .183 

Ferric  Chloride      .                  184 

Liquor  and  Tinctura  Ferri  Chloridi       .        .                 ...  185 

Ferric  Citrate 186 

Liq.  Ferri  Citratis 187 

Ferri  et  Ammonii  Citras 188 

"      "  Potassii  Tartras 188 

"      "  Ammonii  Tartras     .                          188 

Ferri  Phosphas      .         .         .         .         .         .         .         .     "    .         .188 

Ferri  et  Quininse  Citras         »•••••••  189 

Ferri  et  Strychninae  Citras 191 

Ferri  et  Ammonii  Sulphas „  192 

Ferri  Pyrophosphas       .......         0  194 

Ferri  Valerianas             '. 195 

Liq.  Ferri  Acetatis 196 

"       "      Nitratis 197 

"       "      Subsulphatis                           9 198 

"       "      Tersulphatis          ........  199 

Hydrogen  Peroxide,  Estimation  of,  by  Kingzett's  Method  .         .  200 

N 
Table  of  Substances  Estimated  by  —  Sodium  Thiosulphate  V.  S.  201 


PART   II. 

CHAPTER  XIV. 

SANITARY  ANALYSIS  OF  WATER     .        .        .202 

Collection  of  Sample 202 

Color 203 

Odor     ....* 203 

Reaction 204 

Suspended  Matter         •        .        .        .        .         .        .        .        .  204 


Xli  TABLE  OF  CONTENTS. 

PAGE 

Total  Solids ....  204 

Organic  and  Volatile  Matter  or  Loss  on  Ignition          .        .        .  205 

Chlorine 206 

Ammonia       ....  ......  207 

Nessler's  Solution          ......         0         ..  207 

Albuminoid  Ammonia 6  210 

Nitrates 211 

Nitrites 214 

Oxygen-consuming  Power 216 

Phosphates e         .         .         .         .  21? 

Hardness,  Temporary  and  Permanent 219 

Interpretation  of  Results 224 

CHAPTER   XV. 

ESTIMATION  OF  CO2  IN  THE  ATMOSPHERE        .        .  233 
Table  showing  Volume  of  .001  gm.  of  CO8  at  various  Temper- 
atures       237 

CHAPTER  XVI. 

ESTIMATION  OF  ALCOHOL  IN  TINCTURES  AND  BEVERAGES    .  238 
Table  for    Ascertaining    the    Percentages  of  Alcohol   in  Spirit 

from  the  Specific  Gravity ,        .  240 

CHAPTER   XVII. 

ESTIMATION  OF  TANNIN  .  .  .  .  242 

G.  Fleury's  Method        .        .         .        ;        .  •  •  «  «  242 

Lowenthal's  Method      .        .        .        .        .   '  .  .  0  .  243 

CHAPTER  XVIII. 
ESTIMATION  OF  OLEIC  ACID        .        .        .  246 

CHAPTER  XIX. 

ANALYSIS  OF  SOAP         ....  249 

CHAPTER  XX. 
DETERMINATION  OF  THE  MELTING-POINT  OF  FATS   .        .251 

CHAPTER  XXI. 

ESTIMATION  OF  OIL  OR  FAT  IN  EMULSIONS  AND  OINTMENTS.  252 
Soxhlet  Apparatus         ...  253 


TABLE  OF  CONTENTS.  Xlll 

CHAPTER  XXII. 

PAGE 

ESTIMATION  OF  STARCH  IN  CEREALS,  ETC.     .        .  255 

CHAPTER  XXIII. 
ESTIMATION  OF  SUGARS    .        .        .        .259 

CHAPTER  XXIV. 
ESTIMATION  OF  GLYCERIN    .        .        0        .26 

CHAPTER  XXV. 
ESTIMATION  OF  PHENOL     .  266 

Preparation  of  Standard  Bromine  Solution 266 

By  Koppeschaar's  Method     .......  268 

Dr.  Waller's  Method .272 

Assay  of  Crude  Carbolic  Acid 273 

CHAPTER   XXVI. 

PEPSIN 275 

Valuation  of  Pepsin,  U.  S.  P.  Method  .  277 

Bartley's  Method 278 

CHAPTER   XXVII. 
DETERMINATION  OF  THE  DIASTASIC  VALUE  OF  MALT  AND 

PANCREATIC  EXTRACTS     .        .        .        .281 

Robert's  Method 281 

Park,  Davis  &  Co.'s  Method .283 

CHAPTER   XXVIII. 

VOLUMETRIC  ESTIMATION  OF  ALKALOIDS      .        .  285 
Table   showing   the    Behavior  of  Some   of   the   Alkaloids   with 

Indicators 289 

Table  showing  Factor    for  Various   Alkaloids   when   Titrating 

with  —  Acid  V.  S.  .  ....  290 

20 

Estimation  by  Mayer's  Reagent    .         ......  290 

Alkaloidal  Assay  by  Immiscible  Solvents 292 

CHAPTER  XXIX. 

ESTIMATION  OF  ALKALOIDAL  STRENGTH  OF  SCALE  SALTS.       295 
General  Method  for  the  Estimation  of  the  Alkaloidal  Strength  of 

Extracts 295 


xiv  TABLE  OF   CONTENTS. 


Assay  of  Extract  of  Nux  Vomica,  U.  S.  P t  296 

"  "  Extract  of  Opium  ...  0  0  ...  298 

"  "  Tincture  of  "  300 

"      "  Gum  Opium  ,        0        <=        .  301 

"      "  Cinchona,  U.  S.  P.     -    .         .         .         .         .         .         .302 

"      "  Fl.  Extr.  of  Ipecac          .  ...  304 

"  "  Ipecac  Root 306 

Estimation  of  the  Strength  of  Resinous  Drugs     ....  306 

CHAPTER  XXX. 

ESTIMATION  OF  GLUCOSIDES.        .        .        ,  308 

CHAPTER  XXXI. 

Milk      . .        .        .        .309 

Average  Composition    .         .         „         ......  309 

Colostrum 310 

Reaction »•*...  310 

Specific  Gravity 310 

Lactometer 311 

Table  for  Correcting   the  Sp.    Gr.  of  Milk  according   to  Tem- 
perature .         .         .         .         .         .         .         „         .         .312 

Adulterations  of  Milk 313 

Total  Solids  and  Water 313 

Fat,  Adam's  Method 314 

Werner-Schmidt  Method 315 

Calculation  Method       ......         0         „         .  316 

Calculation  of  Per  Cent  of  Added  Water      .         .         .         .         .317 

Total  Proteids .  318 

Milk  Sugar 318 

CHAPTER   XXXII. 

BUTTER 319 

General  Composition     .......<,.  319 

Reichert's  Process  for  the  Detection  of  Foreign  Fats    .         .         .  319 

Rapid  Method  for  the  Detection  of  Oleomargarine       .         .         .  320 

CHAPTER   XXXIII. 

URINE 322 

Reaction  322 


TABLE  OF  CONTENTS.  XV 

PAGE 

Composition ...  322 

Specific  Gravity 324 

Total  Solids 325 

Chlorides       .         .         .     " 326 

Phosphates 327 

Sulphates 327 

Total  Acidity 328 

Urea 329 

Uric  Acid „ 329 

Abnormal  Constituents 33° 

Albumen 33O 

Blood 333 

Pus 333 

Sugar 034 

Bile 338 

Examination  of  Urinary  Deposits         .         .        .                 .        .  339 

Analysis  of  Urinary  Calculi 340 

PART    III. 
GASOMETRIC  ANALYSIS      ....  342 

CHAPTER  XXXIV. 

THE  NITROMETER         ....  342 
Charles'  and  Boyle's  Law 344 

CHAPTER   XXXV. 

ASSAY  OF  SPIRIT  OF  NITROUS  ETHER         .        .  346 

Assay  of  Amyl  Nitrite 349 

"      "  Sodium  Nitrite 350 

Estimation  of  Nitric  Acid  in  Nitrates 350 

CHAPTER  XXXVI. 

ESTIMATION  OF  SOLUBLE  CARBONATES      .        .  352 

CHAPTER  XXXVII. 

ESTIMATION  OF  UREA  IN  URINE    .        .        .  353 
I.  By   Doremus'    Ureometer.     II.    By   the    Gas-tube    Method. 

III.  By  Squibb's  Urea  Apparatus 353 


XVI  TABLE  OF  CONTENTS. 

CHAPTER  XXXVIII. 

PAGE 

HYDROGEN  DIOXIDE*    ....  357 
Its  Assay  by  the  Nitrometer,  and  bySquibb's  Urea  Apparatus     „  357 

APPENDIX. 

INDICATORS 360 

REAGENTS  AND  TEST  SOLUTIONS 369 


A  LIST  OF  ELEMENTS  OCCURRING  IN  VOLUMETRIC 
METHODS,  THEIR  SYMBOLS,  AND  ATOMIC  WEIGHTS. 


Name. 

Exact   Atomic  Weights 
according    to    Meyer 
and  Seubert,  adopted 
by  the  U.  S.  P. 

Approximate 
Atomic  Weights. 

Aluminium-.  ...    . 

Al 
Sb 

27.04 

IIQ  6 

27.0 
1  2O  O 

Arsenic  

As 

74  Q 

7C  o 

Barium 

Ba 

1*^6  O 

1^6  Q 

Bismuth             .  . 

Bi 

208  o 

208  o 

Boron  

B 

JO  Q 

no 

Bromine 

Br 

lu.y 
7O  76 

80  o 

Cadmium               . 

Cd 

III   H 

1  1  T   <> 

Calcium        . 

Ca 

<?Q    QT 

40  o 

Carbon  

c 

II  Q7 

12  O 

Chlorine  

Cl 

•5C     -57 

<1C     A 

Chromium   . 

Cr 

t?2  o 

co  o 

Cooper 

Cu 

62  18 

5^.u 

61  o 

Gold  

Au 

106  7 

106  7 

Hydrogen  

H 

I  O 

I  O 

I 

126.';'? 

126  5 

Fe 

cc  88 

56  o 

Lead 

Pb 

206  4 

2O6  4. 

Lithium  

Li 

7.OI 

7  O 

Magnesium  

M*r 

24  ^ 

2J.  O 

Manganese  

Mn 

CA  8 

ec  o 

Mercury  

Hg 

IQQ.8 

2OO  O 

Nitrogen  .  . 

N 

14  01 

Oxvcren  .  . 

o 

jc  06 

16  o 

Phosphorus  

p 

QO  06 

OT    O 

Platinum         . 

Pt 

IO4.  ^ 

Potassium  .... 

K 

•3Q  O7 

A94-  J 

Silver  

Aff 

107  66 

JV'U 

IO7  7 

Na 

2-J  O 

1U/./ 

2-a  n 

Sr 

87  q 

^SJ.U 

87  •? 

Sulphur       .       ... 

s 

"/•  O 

OT     og 

Tin  

Sn 

118  8 

j^.U 

118  o 

Zinc  

Zn 

6*  i 

6^  o 

xvii 


ABBREVIATIONS  AND  SIGNS, 

Cc cubic  centimetre. 

Gm gramme,  15.43235  grains. 

Gr grain. 

At.  wt. .  .  .  atomic  weight. 

V.  S volumetric  solution. 

T.  S test  solution,  according  to  U.  S.  P. 

U.  S.  P.  .  .  .  United  States  Pharmacopoeia. 

N 

— normal. 

N 

— decmormal. 

10 

centinormal. 

100 

N 

— semi-normal. 

2 

•=-=  or  2N  .  .  double-normal. 

N 

*  means  that  the  figure  is  approximate. 

xviii 


A  TEXT-BOOK 

OF 

VOLUMETRIC  ANALYSIS. 


PART  I. 
INTRODUCTION. 


CHAPTER  I. 

1.  Quantitative  Analysis   is  the   determination  of 
the   proportions  in   which  the  constituents  of  a  com- 
pound are  present. 

The  quantitative  analysis  of  a  substance  may  be 
made  by  the  Gravimetric  Method  or  by  the  Volumetric 
Method. 

2.  The  Gravimetric  Method  consists  in  separating 
and  weighing  the  constituents,  either  in  their  natural 
state  or  in  the  form  of  some  new  and  definite  com- 
pounds the  composition  of  which  is  known  to  the  oper- 
ator, and  from  their  weights  calculating  the  weights  of 
the  original  constituents. 

For  example :  A  silver  solution  is  treated  with  hy- 


2  A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

drochloric  acid  as  long  as  a  precipitate  is  produced. 
This  precipitate  is  thoroughly  washed,  dried,  and 
weighed.  It  consists  of  silver  chloride  143.03  parts, 
which  contain  107.66  parts  (by  weight)  of  metallic  sil- 
ver. 

These  operations  are  often  very  complicated,  require 
great  skill  and  elaborate  apparatus,  besides  consuming 
considerable  time. 

3.  The  Volumetric  Method  is  more  easily  per- 
formed. In  this  the  quantity  of  the  substance  under 
examination  is  ascertained  by  a  calculation  based  upon 
a  measured  quantity  of  a  solution  of  known  strength 
required  to  perform  a  certain  reaction  with  it.  For 
instance,  if  a  silver  solution  is  to  be  analyzed  by  this 
method,  it  is  treated  with  a  solution  of  sodium  chloride 
of  certain  strength  until  no  more  silver  chloride  is  pre- 
cipitated. 

The  sodium-chloride  solution  used  for  this  purpose 

N 
is  a  —  solution,  and  is  made  by  dissolving  one  tenth  of 

the  molecular  weight  in  grammes,  in  sufficient  water  to 
make  one  thousand  cubic  centimetres  (i  litre). 

As  seen  by  the  equation,  one  molecule  of  sodium 
chloride  (58.37  parts  by  weight)  will  precipitate  all  the 
silver  out  of  one  molecule  of  silver  nitrate  (169.55 
parts  by  weight). 

AgN03  +  NaCl  =  AgCl  +  NaNOs. 

169.55          58.37 

N 

Hence    1000  cc.   of  the  —    sodium-chloride   solution 

10 

represent  16.955  grammes  of  silver  nitrate,  and  each  cc. 
precipitates  .016955  gramme. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.  3 

Volumetric  operations  can  be  quickly  performed,  and 
with  great  accuracy. 

The  apparatus  required  is  simple,  and  comparatively 
little  skill  is  necessary.  The  volumetric  method  is 
therefore  to  be  preferred  to  the  gravimetric  whenever 
it  can  be  employed. 

The  solutions  used  are  known  as  volumetric  or  stan- 
dard solutions. 


U1U7BRSITY 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 


CHAPTER   II. 

4.  Standard  and  Normal  Solutions. — When  volu- 
metric analysis  first  came  into  use   the  solutions  were 
so  made  that  each  substance  to  be   estimated   had  its 
own  special  volumetric  solution,  and  this  was  generally 
of  such  strength  as  to  give  the  result  in  percentages. 

Thus  a  certain  strength  of  solution  was  used  for 
testing  soda,  another  for  potassa,  and  a  third  for  am- 
monia. 

These  solutions  were  known  as  normal  solutions, 
and  since  they  are  still  to  some  extent  in  use  it  is  im- 
portant that  no  misconception  should  exist  as  to  what 
a  normal  solution  is.  It  is  to  be  regretted  that  some 
authors  define  a  normal  solution  as  one  having  the 
molecular  weight  in  grammes  of  the  active  reagent  in 
a  litre. 

5.  A   Normal   Solution  is  one  which  contains  in  a 
litre  a  quantity   of  the    active   reagent,   expressed    in 
grammes,  and  chemically  equivalent  to  one  atom  of 
hydrogen. 

6.  A  Standard  Solution  is  any  solution  employed 
in  volumetric  analysis   for  the  purpose   of   estimating 
the  strength  of  substances — that  is,  any  solution  the 
strength  or  chemical  power  of  which  has  been  deter- 
mined.      It    may  be    normal,   decinormal,    or   of    any 
strength  so  long  as  its  strength  is  known.     Such  a  so- 
lution is  said  to  be  "  titrated  "  (French  titre  —  title  or 
power),  sometimes  called  a  "  set "  solution  or  "  stan- 
dardized "  solution. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.  5 

Standard  solutions  for  use  in  volumetric  analysis  are 
usually  solutions  of  acids,  bases,  or  salts,  and  in  two 
cases  elements,  namely,  iodine  and  bromine. 

A  standard  solution  of  a  base  is  usually  used  for  the 
estimation  of  free  acids. 

A  standard  solution  of  afi  acid  is  usually  used  for 
the  estimation  of  a  free  base,  or  the  basic  part  of  a  salt, 
the  acid  of  which  can  be  completely  expelled  by  the 
acid  used  in  the  standard  solution.  Example,  carbo- 
nates. 

A  standard  solution  of  a  salt  may  be  used,  as  a  pre- 
cipitant, or  it  may  be  used  as  an  oxidizing  or  reducing 
agent. 

That  part  of  the  reagent  in  a  standard  solution  which 
reacts  with  the  substance  under  analysis  is  the  active 
constituent  of  the  solution.  As  Ag  in  AgNO3  is  the 
active  constituent  of  the  standard  solution  of  silver 
nitrate, 

AgN03  +  NaCl  =  AgCl  +  NaNO3, 

or  Cl  in  NaCl,  is  the  active  constituent  of  the  standard 
solution  of  sodium  chloride. 

If  the  reagent  is  a  base,  as  KOH,  the  basic  part  K 
is  the  active  constituent.  If  the  reagent  is  an  acid, 
the  active  constituent  is  the  acidulous  part,  as  SO4  in 
H.SO.. 

If  the  action  of  the  reagent  is  oxidizing,  then  that 
part  of  the  reagent  which  produces  the  oxidation  is  the 
active  constituent. 

The  valence  of  an  acid  is  shown  by  the  number  of 
replaceable  hydrogen  atoms  it  contains.  Thus,  HC1  is 
univalent,  H2SO4  is  bivalent ;  which  means  that  a  mole- 
cule of  HC1  is  chemically  equivalent  to  one  atom  of 


6  A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

hydrogen,  and  a  molecule  of  H2SO4  is  chemically 
equivalent  to  two  atoms  of  hydrogen. 

The  valence  of  a  base  is  shown  by  the  number  of 
hydroxyls  it  is  combined  with.  As  KOH  is  univalent, 
Ca(OH),  is  bivalent. 

The  valence  of  a  salt  is  shown  by  the  equivalent  of 
base  which  has  replaced  the  hydrogen  of  the  corre- 
sponding acid. 

Thus  NaCl,  in  which  Na  has  replaced  H  of  HC1,  is 
univalent. 

K,SO4,  in  which  Ka  has  replaced  HQ  of  HaSO4,  is 
bivalent. 

If  a  normal  solution  is  to  be  made  for  a  special  pur- 
pose, its  reaction  in  that  special  case  is  to  be  consid- 
ered. As,  when  K2Cr2O7  is  to  be  used  as  a  precipitat- 
ing agent  its  reaction  is  as  follows : 

2Ba(C2H302)2  +  K2Cr207  +  H2O  = 

2fiaCrO4  +  2KC,H3O2  +  2HC2H3O2. 

It  is  thus  seen  that  one  molecule  of  K2Cr2O7  will 
cause  the  precipitation  of  two  atoms  of  barium  in  the 
form  of  chromate.  Each  atom  of  barium  is  chemically 
equivalent  to  two  atoms  of  hydrogen ;  therefore  one 
fourth  of  a  molecule  of  K.,Cr2O7  is  equivalent  to  one 
atom  of  hydrogen.  And  therefore  a  normal  solution 
of  this  salt  when  used  as  a  precipitating  agent  must 
contain  in  one  litre  one  fourth  of  its  molecular  weight 
in  grammes. 

If  K2CraO7  is  to  be  used  as  an  oxidizing  agent,  the 
three  atoms  of  oxygen  which  it  yields  for  oxidizing 
purposes  must  be  taken  into  account.  When  this  salt 
oxidizes  it  splits  up  into  KaO  +  CraO3  +  O3.  The 
three  atoms  of  oxygen  combine  with  and  oxidize  the 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.  7 

salt  acted  upon,  or  they  combine  with  an  equivalent 
quantity  of  the  hydrogen  of  an  acid  and  liberate  the 
acidulous  part,  which  then  combines  with  the  salt.  As 
the  equations  show, 

6FeO  +  K,Cr,0,  =  K.O  +  Cr.O.  +  3Fe,O.  ; 

6FeSO4  +  K,Cr,0,  +  7H,SO(  = 

7H,0+K,SO.  +  Cr,(SO,)a  +  3Fe,(SO,)!; 

7H,SO.  +  K,Cr,0,  = 

3SO.  +/HaO  +  K.SO.  +  Cr,(SO.)s. 


Each  of  these  atoms  of  oxygen  are  equivalent  to  two 
atoms  of  hydrogen.  Thus  O3  is  equivalent  to  H6. 

Hence  a  litre  of  a  normal  solution  of  K2Cr2O7  ,  when 
used  as  an  oxidizing  agent,  contains  one  sixth  of  its 
molecular  weight  in  grammes. 

The  same  may  be  said  of  potassium  permanganate 
when  used  as  an  oxidizing  agent. 

2KMnO4  has  five  atoms  of  oxygen  which  are  avail- 
able for  oxidizing  purposes,  and  each  of  these  is  capa- 
ble of  taking  two  atoms  of  hydrogen  from  an  acid  and 
liberating  the  acidulous  part.  The  hydrogen  equiva- 
lent of  this  salt  may  therefore  be  said  to  be  one  tenth 
of  the  weight  of  2KMnO4,  and  a  normal  solution  of  this 
salt  contains  31.534  gm.  in  a  litre. 

Sodium  Thiosulphate  (Hyposulphite),  Na2S2O,  ,  is 
another  instance.  The  molecule  of  this  salt  has  two 
atoms  of  sodium,  which  have  replaced  two  atoms  of 
hydrogen  of  thiosulphuric  acid.  Thus  it  would  seem 
that  a  normal  solution  should  contain  one  half  of  the 
molecular  weight  in  grammes.  But  the  particular  re- 
action of  this  salt  with  iodine  is  taken  into  account. 


A   TEXT-BOOK  OF   VOLUMETRIC   ANALYSIS. 

One  molecule  reacts  with  one  atom  of  iodine,  as  seen 
by  the  equation 

2NaaSaO3,  5HaO  +  I,  =  2NaI  +  NaaS4O6  +  ioH3O. 

Since  iodine  is  univalent,  a  molecule  of  the  salt  is 
equivalent  to  one  atom  of  hydrogen. 

A  normal  solution  of  this  salt  therefore  contains  the 
molecular  weight  in  grammes  in  a  litre. 

/N\ 
According  to  the   U.  S.   P.,  Normal  solutions  ( — ) 

are  those  which  contain  in  one  litre  (1000  cc.)  the  mo- 
lecular weight  of  the  active  reagent  in  grammes,  and 
reduced  to  the  valence  corresponding  to  one  atom  of 
replaceable  hydrogen  or  its  equivalent. 

Thus  oxalic  acid  H2C2O4  +  2H2O  —  125.7,  having 
two  replaceable  H  atoms.  One  half  of  its  molecular 
weight  in  grammes  is  contained  in  a  litre  of  its  normal 
solution,  while  hydrochloric  acid  HC1  =  36.37,  which 
has  but  one  replaceable  H  atom,  has  its  full  molecular 
weight  in  grammes  in  a  litre  of  its  normal  solution. 
Sulphuric  acid  H2SO4  has  two  replaceable  H  atoms, 
so  its  normal  solution  contains  one  half  of  its  molecu- 
lar weight  in  grammes  in  a  litre.  NaOH  and  KOH 
being  monobasic,  a  litre  of  a  normal  solution  of  either 
contains  the  full  molecular  weight  of  the  salt  in 
grammes. 

N 

7.  Decinormal    Solutions,  — ,   are  one   tenth   the 

strength  of  normal  solutions. 

N 

8.  Centinormal    Solutions, ,  are  one  hundredth 

100 

the  strength  of  normal  solutions. 


A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.  Q 

N 

9.  Seminormal    Solutions,  — ,    are  one  half    the 

strength  of  normal  solutions. 

10.  Double-normal  Solutions,  -^p    are    twice    the 

strength  of  the  normal. 

11.  Empirical  Solutions   are   those   which   do  not 
contain  an  exact  atomic  proportion  of  reagent,  but  are 
generally  of  such  strength  that  I  cc.  =  o.oi  gm.  of  the 
substance  upon  which  it  acts. 

12.  To  Titrate  a  substance  means  to  test  it  volu- 
metrically  for   the  amount  of  pure   substance  it  con- 
tains.    The  term  is  used  in  preference  to  "  tested  "  or 
"  analyzed,"  because  these  terms   may  relate  to  quali- 
tative examinations  as  well  as  quantitative,  whereas  ti- 
tration applies  only  to  volumetric  analysis. 

13.  Residual  Titration,   Re-titration,    sometimes 
called  Back  Titration,  consists  in  treating  the  substance 
under  examination  with  standard  solution  in  a  quan- 
tity known  to  be  in  excess  of  that  actually  required  ; 
the  excess  (or  residue)  is  then  ascertained  by  residual 
titration  with  another  standard  solution. 

Thus  the  quantity  of  the  first  solution  which  went 
into  combination  is  found. 

Example. — Ammonium  carbonate  is  treated  first  with 

N 

— HaSO4  in  excess,  and  the  excess  then  found  by  ti- 
tration with  —  KOH. 
I 

N 
The  quantity  of  the — KOH  used  is  then  deducted 

N 
from  the  quantity  of  — H2SO4  added,  which  gives   the 

quantity  of  the  latter  which   was   neutralized   by  the 
ammonium  carbonate. 


THUTBBSITtf 


10        A  TEXT-BOOK   OF    VOLUMETRIC  ANALYSIS. 


CHAPTER  III. 

An  Indicator  is  a  substance  which  is  used  in  volu- 
metric analysis,  and  which  indicates  by  change  of  color, 
or  some  other  visible  effect,  the  exact  point  at  which  a 
given  reaction  is  complete. 

Generally  the  indicator  is  added  to  the  substance 
under  examination,  but  in  a  few  cases  it  is  used  along- 
side, a  drop  of  the  substance  being  occasionally  brought 
in  contact  with  a  drop  of  the  indicator. 

Thus  in  estimating  an  alkali  with  an  acid-volumetric 
solution  the  alkali  is  shown  to  be  completely  neutral- 
ized when  the  litmus  tincture  which  was  added  becomes 
faintly  red  or  the  phenolphthalein  colorless.  Again, 
when  haloid  salts  are  estimated  with  nitrate-of-silver 
solution,  chromate  of  potassium  is  added  as  indicator. 
A  white  precipitate  is  produced  as  long  as  any  halogen 
is  present  to  combine  with  the  silver,  and  when  all  is 
precipitated  the  chromate  of  potassium  acts  upon  the 
silver  nitrate,  forming  the  red-silver  chromate,  this 
color  thus  showing  that  all  the  halogen  has  been  pre- 
cipitated. 

INDICATORS. 

The  principal  indicators  used  are  : 

Tincture  of  Litmus,  which  shows  acidity  by  turn- 
ing red  and  alkalinity  by  becoming  blue. 

Phenolphthalein  Solution,  which  is  colorless  in 
acid  solutions  and  red  in  alkaline  solutions,  but  is  not 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         II 

reliable  for  alkaline  phosphates,  bicarbonates,  or  am- 
monia. 

Methyl-orange  Solution  turns  red  with  acids  and 
yellow  with  alkalies.  It  is  not  affected  by  carbonic 
acid,  and  is  therefore  adapted  for  the  titration  of  alka- 
line carbonates. 

Rosolic-acid  Solution  is  yellow  with  acids  and  vio- 
let-red with  alkalies.  It  is  very  sensitive  to  ammonia. 

Tincture  of  Turmeric  turns  brown  with  alkalies, 
and  the  yellow  color  is  restored  by  acids. 

Cochineal  Solution  turns  violet  with  alkalies  and 
yellowish  with  acids.  It  is  used  chiefly  in  the  presence 
of  ammonia  or  alkaline  earths. 

Eosin  Solution  is  red  by  transmitted  light,  and 
shows  a  strong  green  fluorescence  by  reflected  light. 
Acids  destroy  this  fluorescence  and  alkalies  restore  it. 

Brazilwood  Test-solution  turns  purplish  red  with 
alkalies  and  yellow  with  acids. 

Fluorescein  Test-solution  shows  a  strong  green 
fluorescence  by  reflected  light  in  the  presence  of  the 
least  excess  of  an  alkali. 

Neutral  Potassium-chromate  Test-solution  is 
used  in  the  titration  of  haloid  salts  with  silver-nitrate 
solution.  It  indicates  that  all  the  halogen  has  com- 
bined with  the  silver  by  producing  a  red-colored  pre- 
cipitate (silver  chromate). 

Potassiume-ferricyanide  Test-solution  is  used  in 
the  estimation  of  ferrous  salts  with  potassium-dichro- 
mate  solution.  It  gives  a  blue  color  to  a  drop  of  the 
solution  on  a  white  slab  as  long  as  any  iron  salt  is 
present  which  has  not  been  oxidized  to  ferric. 

Many  other  indicators  are  also  used. 


12         A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 


CHAPTER   IV. 

GENERAL   PRINCIPLES   OF   CHEMICAL  COM- 
BINATION  UPON    WHICH   VOLUMETRIC 
ANALYSIS  IS   BASED. 

I.  When  substances  unite  chemically  the  union 
always  takes  place  in  definite  and  invariable  proportions. 
Thus  when  silver  nitrate  and  sodium  chloride  are 
brought  together,  169.55  parts  (by  weight)  of  silver  ni- 
trate and  58.37  parts  (by  weight)  of  sodium  chloride 
will  react  with  each  other,  producing  143.05  parts  of  a 
curdy  white  precipitate  (silver  chloride). 

These  substances  will  react  with  each  other  in  these 
proportions  only. 

If  a  greater  proportion  of  silver  nitrate  than  that 
above  stated  be  added  to  the  sodium  chloride,  only 
the  above  proportion  will  react,  the  excess  remaining 
unchanged. 

The  same  is  true  if  sodium  chloride  be  added  in 
excess  of  the  above  proportions.  For  instance,  if  200 
parts  of  silver  nitrate  be  mixed  with  58.37  parts  of 
sodium  chloride  169.55  parts  only  will  react  with  the 
sodium  chloride,  while  3045  parts  of  silver  nitrate  will 
remain  unchanged.  Again,  when  potassium  hydroxide 
and  sulphuric  acid  are  mixed  potassium  sulphate  is 
formed,  111.98  parts  of  potassium  hydroxide  and  97.82 
parts  of  sulphuric  acid  being  required  for  complete 
neutralization.  These  two  substances  unite  chemically 
in  these  proportions  only. 


A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.          13 

The  equation  is 

2KOH  +  H2SO4  =  K2SO4  +  2H3O. 
111.98       97.82 

In  other  words,  111.98.  parts  of  KOH  will  neutralize 
97.82  parts  of  H2SO4,  and  consequently  97.82  parts  of 
H2SO4  will  neutralize  111.98  parts  of  KOH. 

Oxalic  acid  and  sodium  carbonate  react  upon  each 
other  in  the  proportions  shown  in  the  equation 

H^C204  -  2H20  +  Na2C03  =  Na2C2O4  +  CO,  +  sH2O 
125.7  105.85 

125.7  parts  of  crystallized  oxalic  acid  are  neutralized 
by  105.85  parts  of  anhydrous  sodium  carbonate. 

2.  Definite  chemical  compounds  always  contain  the 
same  elements  in  exactly  the  same  proportions,  the 
proportions  being  those  of  their  atomic  weights,  or 
some  multiple  of  these  weights. 

Thus  sodium  chloride  (NaCl)  contains  23  parts  of 
metallic  sodium  and  35.37  parts  of  chlorine,  these  be- 
ing the  atomic  weights  of  sodium  and  chlorine,  respec- 
tively. 

Potassium  sulphate  (K2SO4)  contains  twice  39.03  — 
78.06  parts  of  potassium,  31.98  parts  of  sulphur,  and 
four  times  15.96  =  63.84  parts  of  oxygen. 

Potassium  hydroxide  (KOH)  contains  39.03  parts  of 
potassium,  15.96  parts  of  oxygen,  and  one  part  of  hy- 
drogen. Hydrochloric  acid  (HC1)  contains  one  part  of 
hydrogen  and  35.37  parts  of  chlorine. 

Upon  these  facts  the  volumetric  methods  of  analysis 
are  based. 

It  has  been  shown  that  97.82  grammes  of  sulphuric 
acid  will  neutralize  111.98  grammes  of  potassium  hy- 


14         A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

droxide  ;  it  is  therefore  evident  that  if  a  solution  of  sul- 
phuric acid  be  made  containing  48.91  grammes  of  the 
pure  acid  in  1000  cc.  that  one  cc.  of  this  solution  will 
neutralize  0.056  gm.  of  potassium  hydroxide.  In  esti- 
mating alkalies  with  this  acid  solution  the  latter  is 
added  from  a  burette,  in  small  portions,  until  the  alkali 
is  neutralized,  as  shown  by  its  reaction  with  some  indi- 
cator. 

Each  cc.  of  the  acid  solution  required  before  neutra- 
lization is  complete  indicates  0.056  gm.  of  KOH,  and 
the  number  of  cc.  used  multiplied  by  0.056  gm.  gives 
the  quantity  of  pure  KOH  in  the  sample  analyzed. 

One  cc.  of  the  same  solution  will  neutralize  0.03996 
gm.  of  sodium  hydroxide  (NaOH),  0.052925  gm.  of 
anhydrous  sodium  carbonate  (Na2COs),  etc. 

If  a  solution  of  crystallized  oxalic  acid  be  made  by 
dissolving  62.85  gm-  m  sufficient  water  to  make  1000  cc., 
we  will  have  a  normal  solution,  the  neutralizing  power 
of  which  is  exactly  equivalent  to  the  above-mentioned 
normal  sulphuric-acid  solution. 

The  strength  of  acids  is  estimated  by  alkali  volumet- 
ric solutions.  A  normal  solution  of  potassium  hydrox- 
ide containing  55.99  gm.  in  the  litre  will  neutralize 
exactly  I  litre  of  the  normal  acid  solution  ;  i  cc.  of  this 
normal  alkali  will  neutralize  0.03637  gm.  of  HCl, 
0.06285  gm.  of  H2C2O4,  or  0.04891  gm.  of  H2SO4,  etc. 


A   TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.          15 


CHAPTER  V. 

WEIGHTS  AND   MEASURES  USED  IN  VOLUMETRIC 
ANALYSIS. 

THE  metric  or  decimal  system  is  used  in  this  country 
and  on  the  continent  in  Europe,  but  in  England  the 
grain  system  is  used. 

The  unit  of  weight  in  the  metric  system  is  the 
gramme  (gm.). 

A  gramme  of  distilled  water  at  its  maximum  density, 
4°  C.  (39°  F.),  measures  one  cubic  centimetre  (cc.). 

A  kilogram  is  1000  gms. 

A  litre  is  1000  cubic  centimetres. 

Volumetric  instruments  are  graduated  in  the  metric 
system,  but  not  at  4°  C.  If  they  were,  it  would  neces- 
sitate the  carrying  out  of  all  volumetric  operations  at 
that  temperature,  and  it  would  be  impossible  to  do 
careful  volumetric  work  except  for  two  or  three  months 
of  the  year,  unless  troublesome  calculations  for  the  cor- 
rection of  volume  were  made. 

For  this  reason  the  temperature  of  15°  C.  (59°  F.)  was 
taken  as  the  standard,  and  at  this  temperature  most 
volumetric  instruments  are  graduated.  In  making  very 
careful  examinations  the  work  should  be  done  at  this 
temperature. 

One  gramme  of  distilled  water  at  I5°C.  measures 
one  cc.  as  used  in  volumetric  analysis. 

The  true  cc.  weighs  at  15°  C.  only  0.999  gm-  Casa- 
major  (C.  N.,  xxxv.  160)  gives  the  following  figures, 


l6         A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

showing   the    relative   contraction    and    expansion    of 
water  below  and  above  I5°C.: 

Degree  C.  Degree  C. 

8  —  .000590        17  +  .000305 

9  —  .000550        1 8  +  .000473 

10  —  .000492        19  -f-  .000652 

1 1  —  .000420  20  +  .000841 

12  —  .OOO334  2I  +  .OOIO39 

13  —  .000236  22  +  .001246 

14  —  .000124  23  -f-  .001462 

15  —  normal  24  +  .001686 
i6+-  000147  25  +  .001919 

By  means  of  these  numbers  it  is  easy  to  calculate 
the  volume  of  liquid  at  15°  C.  corresponding  to  any 
volume  observed  at  any  temperature  between  8°  C.  and 
25°  C.  If  25  cc.  of  solution  had  been  used  at  20°  C., 
the  table  shows  that  I  cc.  of  water  passing  from  15°  to 
20°  is  increased  to  1.000841  cc.  Therefore,  by  dividing 
25  cc.  by  1.000841,  the  quotient,  24.97  cc.,  is  obtained, 
which  represents  the  volume  at  15°  C.  corresponding 
to  25  cc.  at  20°  C. 

These  corrections  are  of  value  only  for  very  dilute 
solutions  and  for  water,  but  useless  for  concentrated 
solutions.  Slight  variations  of  atmospheric  pressure 
may  be  disregarded. 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.          I? 

CHAPTER   VI. 

APPARATUS   USED   IN   VOLUMETRIC   ANALYSES. 

The  Burette  is  a  graduated  glass  tube  which  holds 
from  25  to  100  cc.  and  is  graduated  in  fifths  or  tenths 
of  a  cc.,  and  provided  at  the  lower  end 
with  a  rubber  tube  and  pinch  -  cock. 
The  use  of  this  instrument  is  to  accu- 
rately measure  quantities  of  standard 
solutions  used  in  an  analysis.  It  is  in 
an  upright  position  when  in  use,  and 
the  flow  of  the  solution  can  be  regu- 
lated so  as  to  run  out  in  a  stream  or 
flow  in  drops  by  pressing  the  pinch- 
cock  between  the  thumb  and  forefinger. 
The  quantity  of  solution  used  can  be 
read  from  the  graduation  on  the  out- 
side of  the  tube.  This  is  the 
simplest  and  most  common 
form  of  burette,  and  is  known 
as  Mohr's  (Fig.  i). 

The  greatest  drawback  to 
this  burette  is  that  it  cannot 
be  used  for  permanganate  or 
other  solutions  that  act  upon 
the  rubber.  FlG-  x- 

This  defect  can  be  overcome  by  the  use  of  a  burette 
having  a  glass  stop-cock  in  place  of  the  rubber  tubing 
and  pinch-cock.  This  form  has  the  additional  advan- 
tage of  being  capable  of  delivering  the  solution  in 


1 8         A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

drops  while    both   hands    of   the    operator  are   disen- 
gaged (Fig.  2). 

Another  good  arrangement  is  that  in  which  the  tap 


FIG.  2.  FIG.  3.  FIG.  4. 

is  placed  in  an  oblique  position,  so  that  it  will  not 
easily  drop  out  of  place  (Fig.  3). 

These  glass  stop-cock  burettes  should  be  emptied 
and  washed  immediately  after  use,  especially  if  soda  or 
potassa  solution  has  been  used  ;  for  these  act  upon  the 
glass,  and  often  cause  the  stopper  to  stick  so  firmly 
that  it  cannot  be  turned  or  removed  without  danger  of 
breaking  the  instrument. 

Other   forms   of   burettes   are   Mohrs  Foot  Burette, 


A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 


with  rubber  ball  (Fig.  4).  There  is  a  hole  in  the 
rubber  ball,  and  by  placing  the  thumb  over  the  hole 
and  gently  squeezing,  the  flow  of  the  liquid  may 
be  nicely  regulated. 

Bink's   Burette  (Fig.    5)   is  used  by  holding  in  the 


FIG.  5. 


FIG.  6. 


FIG   60. 


hand  and  inclining  sufficiently  to  allow  the  liquid  to 
flow,  then  placing  in  an  upright  position,  and  reading 
when  the  surface  of  the  liquid  has  settled. 

Gay-Lussacs  (Fig.    6)   must    also    be  inclined  when 
used.      A    wooden    foot   is  generally   provided,    into 


20         A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

which  this  burette  is  placed  to  rest  in  an  upright 
position.  By  inserting  a  tightly-fitting  cork  into  the 
open  end  and  passing  through  this  cork  a  small  bent 
glass  tube,  the  flow  of  the  solution  from  the  exit-tube 
can  be  nicely  regulated  by  blowing  through  the  small 
glass  tube.  The  necessity  for  inclining  the  burette 
is  thus  obviated.  See  Fig.  6a. 

These  two  latter  burettes  being  held  in  the  hand 
when  in  use,  there  is  a  chance  of  increasing  the  bulk 
of  the  fluid  by  the  heat  of  the  body,  thus  leading  to 
incorrect  measurements. 

The  use  of  the  pinch-cock  in  Mohr's  burette  may  be 
dispensed  with  by  introducing  into  the 
rubber  tube  a  small  piece  of  glass  rod, 
which  must  not  fit  too  tightly.  By 
firmly  squeezing  the  rubber  tube  sur- 
rounding  the  glass  rod  a  small  canal  is 
opened,  through  which  the  liquid  es. 
capes.  A  very  delicate  action  can  in  this  way  be 
obtained,  and  the  flow  of  the  liquid  is  completely 
under  the  control  of  the  operator.  (See  Fig.  7.) 

The  Measuring-flask  is  a  vessel  made  of  thin  glass 
having  a  narrow  neck,  and  so  constructed  as  to  hold 
a  definite  amount  of  liquid  when  filled  up  to  the 
mark  on  the  neck.  These  flasks  are  of  various  sizes, 
holding  100,  250,  500,  1000  cc.,  etc.,  but  are  generally 
called  "Litre  Flasks."  (Fig.  8). 

They  are  used  for  making  volumetric  solutions. 

Those  which  have  the  mark  below  the  middle  of  the 
neck  are  to  be  preferred,  because  the  contents  can  be 
more  easily  shaken. 

The  Test  Mixer,  or  Graduated  Cylinder  (Fig.  9),  is 
for  measuring  and  mixing  smaller  quantities  of  solutions. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         21 

They  are  made  of  different  sizes,  holding  100,  250,  500, 
and  1000  cc.,  and  graduated  in  fifths  or  tenths  of  a  cc. 


FIG.  8.  FIG.  9. 

Pipettes  are  of  two  kinds :  those  which  are  marked 
for  one  quantity  only,  and  those  which  are  graduated 
on  the  stem  to  deliver  various  quantities  (Fig.  10  and 
Fig.  100).  Pipettes  are  filled  by  applying  the  mouth 
to  the  upper  end  and  sucking  the  liquid  up  to  the 
mark ;  then  by  placing  the  moistened  forefinger  over 
the  upper  opening  the  liquid  is  prevented  from  run- 
ning out,  but  may  be  delivered  in  drops  or  allowed 
to  run  out  to  any  mark  by  loosening  the  finger. 

A  very  convenient  form  of  pipette  is  one  which  has 
attached  to  its  upper  end  a  piece  of  rubber  tubing, 
into  which  a  piece  of  glass  rod  has  been  inserted. 


22 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


By  squeezing  the  rubber  surrounding  the  glass  rod 
firmly  between  the  fingers  a  canal  is  opened,  and  the 
liquid  can  be  drawn  up  into  the  pipette  by  suction 
with  the  lips.  Then  by  gentle  pressure  the  liquid  can 
be  allowed  to  run  out  slowly,  and  stopped  at  any 
point  by  removing  the  pressure  (Fig.  11). 

The  Nipple  Pipette  is  very  convenient   for   measur- 


50  CO 


10  CC 


FIG.  10. 


FIG.  i off. 


FIG.  n. 


flG.    12. 


ing  small  quantities  of  liquids,  such  as  I  or  2  cc.  (Fig.  12). 

When  a  volatile  or  highly  poisonous  solution  is  to 

be  measured  it  is  not  advisable  to  suck  it  up  with  the 

mouth.     The  pipette  may  then  be  filled  by  dipping  it 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         23 

into  the  liquid  contained  in  a  long,  narrow  vessel  until 
the  liquid  reaches  the  proper  mark  on  the  pipette, 
then  closing  the  upper  opening  and  withdrawing. 


FIG.  13. 

When  this  is  done  the  liquid  which  adheres  to  the 
outside  of  the  pipette  should  be  dried  off  before  the 
measured  liquid  is  delivered. 


24         A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

When  a  number  of  estimations  are  to  be  made  in 
which  the  same  volumetric  solution  is  employed,  the 
arrangement  shown  in  Figs.  13  and  14  is  very  ser- 
viceable. 

A  T-shaped  glass  tube  is  inserted  between  the  lower 
end  of  the  burette  and  the  pinch-cock  and  connected 


FIG.  14. 

by  a  rubber  tube  with  a  reservoir  containing  the  volu- 
metric solution.  The  tube  which  communicates  with 
the  reservoir  is  provided  with  a  pinch-cock,  which  when 
open  allows  the  solution  to  flow  into  and  fill  the  burette 
in  so  gradual  a  manner  that  no  bubbles  are  formed. 
The  burette  is  emptied  in  the  usual  manner. 

If  the  titration  is  to  be  conducted  at  a  high  temper- 
ature, as  in  the  estimation  of  carbonates,  when  litmus 
is  used  as  the  indicator,  or  in  the  estimation  of  sugar 


A   TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.         2$ 

by  copper  solution,  a  long  rubber  tube  should  be 
attached  to  the  lower  end  of  the  burette.  The  boiling 
can  then  be  done  at  a  little  distance,  and  the  expansion 


FIG.  15. 

of  the  liquid  in  the  burette  avoided.     The  pinch-cock 
is  fixed  about  midway  on  the  tube. 


FIG.  16. 


The  burette  support  represented   in   Fig.    15,  with 
heavy  tripod  base,  is  one  of  the  best  for  one  or  two 


26 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 


burettes.       It  stands    firmly  upon  an  uneven  surface, 
and  does  not  easily  tip  over. 

If  two  burettes  are  to  be  supported  the  clamp  shown 


FIG.  17. 

in  Fig.  16  may  be  used.     Fig.  17  represents  a  revolving 
burette-holder  for  eight  burettes. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         27 


CHAPTER  VII. 
ON  THE   USE  OF  APPARATUS, 

It  is  important  that  all  apparatus  used  in  volumetric 
analysis  should  be  perfectly  clean.  Even  new  appara- 
tus should  be  cleansed  by  passing  dilute  hydrochloric 
acid  through  them  and  then  rinsing  with  distilled  water. 

If  the  burette,  pipette,  or  other  instrument  is  even 
slightly  greasy,  the  liquid  will  not  flow  smoothly,  and 
drops  of  the  liquid  will  remain  adhering  to  the  sides, 
thus  leading  to  inaccurate  results. 

Greasiness  may  be  removed  with  dilute  soda  solution. 
If  this  fails  the  instrument  should  be  allowed  to  remain 
for  some  little  time  in  a  solution  containing  sulphuric 
acid  and  potassium  dichromate,  which  will  radically 
remove  all  traces  of  grease. 

The  burette  or  other  measuring  instruments  should 
never  be  rilled  with  volumetric  solution  without  first 
rinsing,  even  if  the  burette  be  perfectly  dry. 

It  is  well  to  wash  the  inside  of  the  instrument  with 
two  or  three  small  portions  of  the  solution  with  which 
it  is  to  be  filled. 

The  burette  may  be  filled  with  the  aid  of  a  funnel, 
the  stem  of  which  should  be  placed  against  the  inner 
wall  of  the  burette  so  that  the  solution  will  flow  down 
the  side  and  thus  prevent  the  formation  of  bubbles. 

The  burette  should  be  filled  to  above  the  zero  mark, 


28         A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

and  the  air-bubbles,  if  there  are  any,  removed  by  gently 
tapping  with  the  finger. 

A  portion  of  the  liquid  should  then  be  allowed  to 
run  out  in  a  stream  so  that  no  air-bubbles  remain  in 
the  lower  part  of  the  burette.  In  the  glass  tap  burette 
it  can  be  easily  seen  if  any  air  is  present,  but  in  the 
pinch-cock  burette  it  is  sometimes  necessary  to  take 
hold  of  the  rubber  tube  between  the  thumb  and  fore- 
finger and  gently  stroke  upward.  Or  the  glass  nip  at 
the  lower  end  of  the  burette  may  be  pointed  upward, 
and  the  pinch-cock  opened  wide  so  that  a  stream  of 
the  liquid  will  pass  through  and  force  out  any  air  that 
may  be  inclosed. 

ON   THE   READING   OF   INSTRUMENTS. 

In  narrow  vessels  the  surfaces  of  liquids  are  never 

^    -  ^  i    level.     This  is  owing  to  the  capillary  attrac- 

|   tion  exerted  by  the  sides  of  the  vessel  upon 

I   the  liquid,  drawing  the  edge  up  and  forming 

I   a  saucerlike  concavity  (Fig.  18).      All  liquids 

^vamaK^.  ,   .  e 

I   present  this  concave  surface  except  mercury, 
the  surface  of  which  is  convex. 

This  behavior  of  liquids  makes  it  difficult 

to  find  a  distinct  level,  and    in   reading  the 

F        g    measure  either  the  upper  meniscus  (a)  or  the 

lower  meniscus  (b)  may  be  used  (Fig.  19). 
The  most  satisfactory  results  are  obtained  if  the  low- 
est point  of  the  curve  (b)  is  used,  especially  with  light- 
colored  solutions.  But  if  dark-colored  or  opaque  solu- 
tions are  measured,  it  is  necessary  to  use  the  upper 
meniscus  (a)  for  reading. 

In  all  cases  the  eye  should   be  brought  on  a  level 


ITT 


A   TEXT-BOOK   OF    VOUJ METRIC   ANALYSIS.         29 

with  the  surface  of  the  liquid  in  reading  the  gradua- 
tion. 

The  eye  is  very  much  assisted  by  using  a  small  card, 
the  lower  half  of  which  is  black  and  the  upper  half 
white.  This  card  is  held  behind  the  burette,  the 
dividing  line  between  white  and  black  being  about  an 
eighth  of  an  inch  below  the  surface  of  the  liquid.  The 


FIG.  19. 


FIG    20. 


FIG.  21. 


eye  is  then  brought  on  a  level  with  it,  and  the  lower 
meniscus  can  be  distinctly  seen  as  a  sharply-defined 
black  line  against  the  white  background  (Fig.  20). 

Erdman's  Float,  Fig.  21,  is  an  elongated  glass  bulb, 
which  is  weighted  at  its  lower  end  with  mercury,  to 
keep  it  in  an  upright  position  when  floating.  It  is  of 
such  diameter  that  it  will  slide  easily  up  and  down 


30         A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

inside  of  a  burette.  There  is  a  ring  at  the  top  by 
which  it  can  be  lifted  in  or  out  by  means  of  a  bent 
wire.  Around  its  centre  a  line  is  marked.  At  this 
line  instead  of  at  the  meniscus  the  reading  is  taken. 

These  floats  are  sometimes  provided  with  a  thermo- 
meter, and  they  then  register  the  temperature  as  well 
as  the  volume. 

Litre  flasks  are  sometimes  made  with  two  marks  on 
the  neck  very  near  together;  the  lower  one  is  the 
litre-mark.  If  the  flask  is  required  to  deliver  a  litre,  it 
must  be  filled  to  the  upper  mark ;  the  difference  be- 
tween the  two  measures  being  the  equivalent  of  the 
liquid  which  remains  in  the  flask,  adhering  to  the  sides. 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS,         31 


CHAPTER  VIII. 
METHODS  OF   CALCULATING   RESULTS. 

N 

EACH  cc.  of  a—  uruvalent  volumetric  solution  con- 
i 

tains  1  0*0  0-  of  the  molecular  weight  in  grammes  of  its 
reagent,  and  will  neutralize  ToV<r  °f  tne  molecular 
weight  of  a  univalent  substance,  or  ^-oVo"  of  the  molec- 
ular weight  of  a  bivalent  substance. 

N 

Each  cc.  of  a  —  bivalent  volumetric  solution  contains 
i 


of  the  molecular  weight  in  grammes  of  its  reagent, 
and  will  neutralize  or  combine  with  ^oinr  °f  tne  molec- 
ular weight  of  a  bivalent  salt,  or  TirVo"  °f  tne  molec- 
ular weight  of  a  univalent  salt. 

N 
A  —  is  only  -fa  the  strength  of  a  normal  solution  and 

will  neutralize  only  y1^  the  quantity  of  salt,  etc. 

Normal  and  decinormal  solutions  of  acids  should 
neutralize  normal  and  decinormal  solutions  of  alkalis, 
volume  for  volume.  Decinormal  solution  of  silver  ni- 
trate and  decinormal  solution  of  hydrochloric  acid  or 
sodium  chloride  should  combine  volume  for  volume, 
etc. 

The  Rules  for  Obtaining  the  Percentage  of  pure 
substance  in  any  commercial  article,  such  as  acids,  al- 
kalis, and  various  salts,  are  : 


32         A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

1.  With  normal  solutions  -^   or  -fa  (according  to  its 
atomicity)  of  the  molecular  weight  in  grammes  of  the 
substance  is  weighed  for  titration,  and  the  number  of 
cc.  of  the  V.  S.  required  to  produce  the  desired  reaction 
is  the    percentage  of  the  substance  whose   molecular 
weight  has  been  used. 

Thus,  if  sodium  hydroxide  (NaOH)  is  to  be  exam- 
ined by  titration  with  a  normal  acid  solution  -^  of  its 
molecular  weight  in  grammes,  4  gms.  is  weighed  out, 
and  each  cc.  of  the  acid  solution  required  represents 
\%  of  the  pure  salt. 

If  sodium  carbonate  (Na2CO3)  is  to  be  tritated  -fa  of 
its  molecular  weight  in  grammes,  5.3  gms.  is  taken. 

2.  With  decinormal  solutions  T^-Q  or  -^-^  of  the 
lecular  weight  in  grammes  of  the  substance  to  be  ana- 
lyzed is  taken,  and  the  number  of  cc.  will,  in  like  man- 
ner, give  the  percentage. 

The  following  equations  will  serve  to  explain  more 
fully : 

N 
Sodium  hydroxide  with  —  sulphuric  acid: 

2NaOH  +  H2SO4  =  Na2SO4  +  2H2O. 

2  X  40  =  80  2)98 

10)40  49  =  to  1000  cc. 

4.0  gms  =  to    100  cc. 

Sodium  carbonate  with  —  sulphuric  acid: 

Na,C03  +  H2S04  =  Na2S04  +  H2O  +  CO2. 

2)98 

20)106  49  =  to  1000  cc. 

5. 3  gms.  =  to    100  cc. 


A  TEXT- BOOK   OF   VOLUMETRIC   ANALYSIS.          33 

N 

With  —  sulphuric  acid  : 
10 

2NaOH  +  H2S04  =  Na3SO4  +  2H,O. 

2  X  40  =  80        2)98 

100)40  49       =  to  1000  cc. 

0.40  gms.  =  to    100  cc. 

3.  Factors  or  coefficients  for  calculating  the  analy- 
ses.—It  frequently  occurs  that  from  the  nature  of  the 
substance,  or  from  its  being  in  solution,  this  percentage 
method  cannot  be  conveniently  followed. 

The  best  way  to  proceed  in  such  a  case  is  to  find 
the  factor. 

The  first  step  in  all  cases  is  to  write  the  equation 
for  the  reaction  which  takes  place  between  the  sub- 
stance under  analysis  and  the  solution  used. 

For  instance,  a  solution  of  caustic  potash  is  to  be 

N 
examined,  a  —  solution  of  sulphuric  acid  being  used. 

2KOH  +  H2S04  =  KaS04  +  2H20. 

2)112  2)98  N 

56  49       =  to  1000  cc.  —  acid. 

o.s6gm.        .049       =  to         ice.  — acid. 

N 

The  factor  for   KOH  when  —  solution    is   used    is 

i 

.056  gm.,  that  being  the  quantity  neutralized  by  each 

N  N 

cc.  of  the  —  acid.       If  —  acid  were  used  the  factor 

I  10 

would  be  .0056  gm. 

The  number  of  cc.  of  the  acid  used  to  produce  the 
desired  result,  when  multiplied  by  the  factor  gives  the 
quantity  in  grammes  of  KOH  in  the  solution  taken. 


34         A  TEXT-BOOK    OF  VOLUMETRIC   ANALYSIS. 

Example.  —  If  10    grammes    of    caustic-potash    solu- 

N 
tion  were  taken,  and  40  cc.  of  --  acid  were  required, 

the  logms.  of  solution  contained  .056  gm.  X  40  =  2.24 
gms.  of  pure  KOH. 

To  find  the  percentage,  the  following  formula  may 
be  used. 

X  IPO        , 


W 


Q  =  the  quantity  of  pure  substance  found  by  calcula- 
tion; 

W  =  weight  of  substance  taken. 
If  the  above  example  is  taken,  we  have 


Or  the  calculation  may  be  made  by  proportion. 

The  quantity  of  the  substance  taken  is  always  the 
first  term,  and  the  quantity  of  pure  substance  found, 
the  second  term. 

The  following  rule  is  easily  remembered  :  As  the 
quantity  taken  is  to  the  quantity  found,  so  is  100  to  x, 
the  percentage  of  pure  substance  in  tJie  sample. 

Three  terms  of  the  equation  being  given,  the  fourth 
is  found  by  multiplying  the  means  and  dividing  the 
product  by  the  given  extreme.  By  applying  this  rule 
to  the  above  case  we  have 

IO  :  2.24  :  :  100  :  x.         x  =  22.4$. 


A   TEXT-BOOK    OF  VOLUMETRIC   ANALYSIS. 


35 


TABLE  SHOWING  THE  APPROXIMATE  NORMAL  FACTORS,  ETC.,  OF 
THE  ALKALIES,  ALKALINE  EARTHS,  AND  ACIDS. 


Substance. 

Formula. 

Molec- 
ular 
Weight. 

Normal 
Factor.* 

Sodium  hydroxide.                «          >  •  •  • 

NaOH 

o  040 

Na2CO3 

1  06 

OOC'I 

NaHCO3 

8/1 

o  084 

KOH 

*6 

o  056 

Potassium  carbonate                  > 

KoCO, 

1  08 

o  060 

Potassium  bicarbonate       

KHCO3 

IOO 

O    IOO 

Ammonia  (gas)      .  .            . 

NH3 

17 

o  017 

Ammonium  carbonate,  normal  .    ... 
Ammonium  carbonate,  commercial.. 
Linr*                         .        ....                . 

(NH4)2C03 

NsHnCa06 
CaO 

96 
157 

c0 

0.048 

0.052i 

o  028 

Calcium  hydroxide      .         

Ca(OH)2 

7J. 

OO17 

CaCO3 

IOO 

o  050 

HNO3 

A-j 

Hydrochloric  acid                . 

HC1 

UJ 

•76    A 

Sulphuric  acid         -.  . 

H2SO4 

08 

Oxalic  acid    crystallized     

H2C2O4  2H2O 

y° 
126 

o  063 

Acetic  acid  

HC2H3O2 

60 

o  060 

*  This  is  the  coefficient  by  which  the  number  of  cc.  of  normal  solu- 
tion used  is  to  be  multiplied  in  order  to  obtain  the  quantity  of  pure 
substance  present  in  the  material  examined. 


36         A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 


CHAPTER  IX. 
ANALYSIS  BY  NEUTRALIZATION. 

THIS  is  based  upon  the  fact  that  acids  are  neutralized 
by  alkalies  and  alkalies  by  acids. 

The  strength  of  an  acid  is  estimated  by  the  quantity 
of  alkali  that  is  required  to  neutralize  it.  This  process 
is  called  acidimetry. 

The  strength  of  an  alkali  is  found  by  the  quantity  of 
an  acid  that  is  required  to  neutralize  it.  This  process 
is  called  alkalimetry.  The  stronger  the  acid,  the  more 
alkali  is  required,  and  vice  versa. 

A  substance  is  said  to  be  alkaline  when  it  turns  red 
litmus  blue;  phenolphthalein,  red;  turmeric,  brown; 
etc.  Acid,  when  it  turns  blue  litmus  red;  red  phenol- 
phthalein, colorless,  etc. 

The  principal  alkaline  substances  are  the  hydroxides 
and  carbonates  of  sodium,  potassium,  and  ammonium, 
and  the  hydroxides  and  oxides  of  calcium,  barium,  and 
strontium,  and  the  alkaloids. 

When  an  acid  is  brought  in  contact  with  an  alkali 
combination  takes  place,  and  a  neutral  salt  is  formed. 
This  combination  takes  place  in  definite  and  invariable 
proportions  ;  thus  :  If  1 12  parts  of  potassium  hydroxide 
are  mixed  with  98  parts  of  absolute  sulphuric  acid  the 
alkali  as  well  as  the  acid  will  be  neutralized.  If  only 
80  parts  of  the  acid  have  been  added  the  mixture 
would  still  be  alkaline,  for  it  requires  98  parts  of  the 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.         37 

acid  to  neutralize  it.  If  more  than  98  of  the  acid  have 
been  added  the  mixture  would  consist  of  potassium 
sulphate  and  free  sulphuric  acid.  The  reaction  is  thus 
illustrated  : 


2KOH  +  H,SO4  =  K2S04  +  2H20. 

O-™ 


H,=     2 


02  =  32        S    =3 
H,  =*J       04  =  64 

112  98 

Sodium  hydroxide  will  unite  with  oxalic,  and  form  a 
neutral  compound  in  the  proportion  of  80  parts  by 
weight  of  the  former  and  126  parts  by  weight  of  the 
latter,  as  the  equation  shows  : 

2NaOH  +  H2C204  .  2H2O  =  Na2C2O4  +  4H2O. 

2Na  =  46      6H  =    6 

2O      =32         2C    =  24 

2H    =    2      6O  =  96 
80  126 

NH4OH  +  HC1  =  NH4C1  +  H2O. 

N  =  14     H  =     i. 
5H=     5     01  =  35-4 


35  3^.4 

Ammonium  Hydrochloric 

hydroxide.  acid. 

Na2CO3  +  2HC1  =  2NaCl  +  H,O  +  CO2 
106  72.8 

Sodium  carbonate. 


38         A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

Upon  a  careful  perusal  of  the  foregoing  equations  it 
will  be  seen  that  since  definite  weights  of  acids  neu- 
tralize definite  weights  of  alkalies  the  quantity  of  a 
certain  alkali  in  solution  can  be  easily  determined  by 
the  quantity  of  an  acid  solution  of  known  strength  re- 
quired to  neutralize  it,  and  vice  versa. 

If  we  make  a  solution  of  oxalic  acid  of  such  strength 
that  IOOO  cc.  of  it  contains  63  gms.  of  the  crystallized 
acid,  i  cc.  of  it  will  neutralize  .056  gm.  of  KOH,  .040 
gm.  of  NaOH,  or  .035  gm.  of  NH4OH. 

Thus  if  10  gms.  of  solution  of  KOH  be  treated  with 
this  oxalic-acid  solution  and  it  is  found  that  25  cc.  of  it 
are  required  to  neutralize  the  alkali,  the  alkali  solution 
contains  25  x  .056  =  1.4  gms.  of  pure  KOH. 

Since  the  acid  and  alkali  as  well  as  the  neutral  salt 
which  is  formed  are  colorless,  and  no  visible  change 
takes  place  during  the  reaction,  it  is  necessary  to  add 
some  substance  which  by  change  of  color  will  show 
when  the  neutralization  is  complete.  Such  a  substance 
is  known  as  an  indicator.  A  number  of  these  are 
spoken  of  on  page  10. 

Neutralization  is  sometimes  called  saturation. 

ALKALIMETRY. 

Preparation  of  Acid  Volumetric  Solutions. — It  is 
possible  to  carry  out  the  titration  of  most  alkalies  with 
only  one  standard  acid  solution,  but  the  standard  acids 
are  frequently  required  in  other  processes  besides 
mere  saturation,  and  it  is  therefore  advisable  to  have  a 
variety. 

The  standard  oxalic  acid  is  preferred  by  some  be- 
cause of  the  ease  with  which  it  may  be  prepared,  pro- 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.          39 

vided  a  pure  acid  can  be  had.  It  does  not,  however, 
keep  very  long,  and  when  used  for  titrating  carbonates 
with  methyl  orange  as  an  indicator  the  end  reaction  is 
not  very  distinct.  Oxalic  acid  cannot  very  well  be 
used  for  the  titration  of  alkaline  earths,  since  it  forms 
insoluble  compounds  with  these  metals. 

Sulphuric  acid  V.  S.  is  preferred  by  others.  A  pure 
acid  can  be  gotten  without  difficulty,  and  the  standard 
solution  made  with  it  is  totally  unaffected  by  boiling, 
which  cannot  be  said  of  either  nitric  or  hydrochloric 
acid.  Sulphuric  acid,  however,  forms  with  alkaline 
earths  insoluble  compounds.  For  this  reason  standard 
solution  of  hydrochloric  acid  must  frequently  be  em- 
ployed. 

Normal  Oxalic  Acid  V.  S.,  U.  S.  P.—  HaC2O4  + 


2H,O  =  125.7.     *'         gms.  in  i  litre. 


Dissolve  62.85  gms-  (*63  gms.)  of  pure  oxalic  acid 
(see  below)  in  enough  water  to  make,  at  or  near  15°  C., 
exactly  1000  cc. 

Pure  oxalic  acid,  crystallized,  is  in  the  form  of 
colorless,  transparent,  clinorhombic  crystals,  which 
should  leave  no  residue  when  ignited  upon  platinum 
foil.  It  is  completely  soluble  in  14  parts  of  water  at 
15°  C.  If  the  acid  leaves  a  residue  on  ignition  it 
should  be  purified  by  recrystallization,  as  directed  by 
the  U.  S.  P. 

N 
I  cc.  of  —  oxalic  acid  V.  S.  is  the  equivalent  of  — 

NaOH  ....................  0.03996  gm. 

KOH  ....................   0.05599     " 

NH,  .....................  0.01701     " 


40         A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

Decinormal  Oxalic  Acid  V.  S.,  U.  S.  P.— H3C2O4 

+  2H20  =  125.7.        ' 5     Sms-  in  *  litre- 


Dissolve  6.285  gms-  (*&3  gms.)  of  pure  oxalic  acid  in 
enough  water  to  make,  at  or  near  15°  C.,  exactly 
1000  cc. 

N 

I  cc.  of  —  oxalic  acid  V.  S.  is  the  equivalent  of — 
10 

NH3 0.001701  gm. 

KOH 0.005599     " 

NaOH 0.003996     " 

Normal   Hydrochloric    Acid    V.    S.,  U.   S.    P.— 

HC1  =  36.37.     3|.37  |  gms>  in  j  litre> 

Mix  130  cc.  of  hydrochloric  acid  of  sp.  gr.  1.163, 
with  enough  water  to  measure,  at  or  near  15°  C., 
1000  cc. 

Of  this  liquid  (which  is  still  too  concentrated)  meas- 
ure carefully  into  a  flask  10  cc.,  add  a  few  drops  of 
phenolphthalein  T.  S.,  and  gradually  add  from  a  burette 

N 

-  potassium  hydroxide  V.  S.  until  a  permanent  pale 

N 
pink  tint  is  produced.     Note  the  number  of  cc.  of  - 

potassium-hydroxide    solution    consumed,    and    then 
dilute  the  acid  so  that  equal  volumes  of  this  and  the 

N 

-  KOH  V.  S.  neutralize  each  other. 
i 

Example. — Assuming   that   the    10   cc.    of  the  acid 

N 
solution  required  12  cc.  of  the  —  KOH,  each  10  cc.  of 


A   TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.         4! 

the  acid  must  be  diluted  to  12  cc.,  or  the  whole  of  the 
remaining  acid  in  the  same  proportion. 

After  the  dilution  a  new  trial  should  be  made.  10  cc. 
of  the  acid  V.  S.  should  require  exactly  10  cc.  of  the 
alkali. 

This  solution  is  exactly  equivalent  in  neutralizing 

N 
power  to  —  oxalic  acid  V.S. 

Normal  Sulphuric  Acid  V.  S.,  U.  S.  P.—  H2SO4  = 

97.82.          S.91     gms>  in 


Mix  carefully  30  cc.  of  pure  concentrated  sulphuric 
acid  (sp.  gr.  1.835)  with  enough  water  to  make  about 
1050  cc.,  and  allow  the  liquid  to  cool  to  about 
i5°C. 

Titrate  10  cc.  of  this  liquid  in  the  manner  described 

N 
under  —  hydrochloric  acid,  and  dilute  it  so  that  equal 

volumes  of  the  acid  and  the  alkali  will  neutralize  each 
other. 

Note.  —  It  is  recommended  in  the  U.  S.  P.  that  when 
a  normal  acid  solution  is  required  the  normal  sul- 

N 
phuric  acid  should  be  employed  in  place  of  —  oxalic. 

The  oxalic-acid  solution  has  a  tendency  to  crystallize 
on  the  point  of  the  burette. 
Decinormal    Sulphuric  Acid  V.   S.,    U.   S.   P.  — 


H2S04  =  97.82.       .  gms.  in  a  litre. 

Dilute  10  cc.  of  the  normal  sulphuric-acid  solution 
with  enough  water  to  make  100  cc. 

The  standardization  of  normal  acid  solutions   may 


42         A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

also  be  effected  by  the  use  of  pure  anhydrous  sodium 
carbonate. 

Pure  anhydrous  sodium  carbonate  may  be  obtained 
by  heating  to  dull  redness  a  few  grammes  of  pure 
sodium  bicarbonate  for  about  15  minutes.  The  result- 
ing carbonate  is  practically  free  from  impurity. 

The  sodium  bicarbonate  loses  on  ignition  one  half 
of  its  carbonic  acid  gas: 

2NaHCO3  +  Heat  =  NaaCO3  +  COa  +  HaO. 

The  bicarbonate  should,  however,  be  tested  before 
igniting,  and  if  more  than  traces  of  chloride,  sulphate, 
or  thiosulphate  are  found,  these  may  be  removed  by 
washing  a  few  hundred  grammes,  first  with  a  saturated 
solution  of  sodium  bicarbonate,  and  afterward  with 
distilled  water. 

0.53  gm.  of  the  pure  anhydrous  sodium  carbonate 
is  accurately  weighed  and  dissolved  in  about  20  cc.  of 
water  in  a  flask  and  a  few  drops  of  methyl  orange  T.  S. 
added  as  indicator.  The  acid  to  be  "  set "  or  "  stan- 
dardized "  is  then  run  into  the  sodium-carbonate  solu- 
tion until  a  permanent  light-red  color  is  produced.  It 

N 
should  require  exactly  IO  cc.  of  the  y  acid  solution. 

If  8  cc.  of  the  acid  solution  are  consumed  to  bring 
about  the  required  result,  then  every  8  cc.  must  be 
diluted  to  10  cc.,  or  the  whole  of  the  remaining  solu- 
tion must  be  diluted  in  this  proportion  : 

Na,C03  +  H2S04  =  Na2S04  +  H2O  +  COa. 
2)106  2)98  N 

53  gms.  49        =  to  1000  cc.  --V.  S. ; 

0-53  gm-  =  to       I0  cc    l 


A  TEXT- BOOK   OF  VOLUMETRIC   ANALYSIS.         43 

Instead  of  methyl  orange,  litmus  tincture  may  be 
used.  The  carbonic-acid  gas  which  is  liberated  in  this 
reaction  turns  litmus  red;  the  contents  of  the  flask 
should  therefore  be  boiled  for  a  few  minutes  to  drive 
off  the  CO2,  when  the  blue  color  will  return.  More 
acid  is  then  run  in  until  the  mixture  after  boiling 
remains  of  a  neutral  color ;  indicating  that  just  enough 
acid  has  been  added  to  complete  the  reaction  expressed 
in  the  foregoing  equation. 


ESTIMATION   OF  ALKALINE   HYDROXIDES. 

A  definite  quantity  of  the  substance  is  taken  (gen- 
erally weighed),  and  diluted  with  or  dissolved  in  a 
little  water  in  a  flask  or  beaker.  A  few  drops  of  a 
suitable  indicator  are  now  added,  and  the  standard 
acid  solution  allowed  to  flow  in  until  the  last  drop 
added  just  causes  the  color  to  change,  the  flask  being 
agitated  after  each  addition  of  the  acid  solution. 

Potassa.     KOH  *  |^9  u.  S.  P.— Weigh  carefully 

i  gm.  of  potassa,  dissolve  it  in  a  small  quantity  of 
water,  add  a  drop  of  phenolphtalein  solution  as  indi- 

N 
cator,  and  titrate  with  —  sulphuric  acid  V.  S.  until  the 

red  color  just  disappears.  Each  cc.  of  the  normal  acid 
solution  used  represents  .056  gm.  of  pure  potassa.  To 
find  percentage,  multiply  the  factor  (.056)  by  the  num- 

N 

ber  of  cc.  of  —  V.  S.  used,  and  then  multiply  the  prod- 
uct by  100.  Potassium  hydroxide  having  great  affinity 
for  carbonic-acid  gas,  which  it  absorbs  out  of  the  air, 
generally  contains  small  quantities  of  carbonate.  There- 


44         A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

fore  in  titrating  as  above  described  it  should  be  boiled 
once  or  twice  toward  the  end  of  the  reaction  in  order 
to  drive  off  any  CO2  which  may  be  present.  This  gas, 
which  has  an  acid  reaction  with  phenolphtalein,  would 
otherwise  cause  an  incorrect  estimation.  This  precau- 
tion should  be  taken  with  the  other  alkaline  hydroxides. 
The  U.  S.  P.  requirement  is  that  0.56  gm.  of  potassa 
be  neutralized  by  not  less  than  9  cc.  of  the  normal 
acid  solution,  each  cc.  corresponding  to  10  per  cent  of 
pure  potassium  hydroxide.  The  equation  is 

2KOH  +  H2S04  =  K2S04  +  H20. 

2)112  2)98  N 

56  gms.  —     49  gms.  in  1000  cc.  of  —V.  S. 

This  shows  that  56  gms.  of  KOH  are  neutralized  by 

1000  cc.  of  —  V.  S. 
I 

Each  cc.  of  this  solution  will  therefore  neutralize 
0.056  gm.  of  KOH. 

Liquor  Potassa,  U.  S.  P. — This  is  an  aqueous  solu- 
tion of  potassium  hydroxide  (KOH)  containing  about 
5  per  cent  of  the  hydroxide. 

It  is  estimated  volumetrically  in  the  same  manner  as 
potassa,  10  gms.  of  the  solution  of  potassa  being  taken, 

N 
each  cc.  of  the  —  V.  S.  representing  0.056  gm.  of  KOH. 

By  multiplying  the  factor  by  the  number  of  cc.  of 

N 
-  V.  S.  used,  the  quantity  of  absolute  KOH  in  the  10 

gms.  of  liquor  taken  is  obtained. 

The  percentage  is  then  found  by  multiplying  the 
quantity  so  obtained  by  100  and  dividing  by  the  num- 
ber of  grammes  of  the  liquor  taken. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         45 

N 
Thus  if  9  cc.  of  the  —  V.  S.  were  used,  the  10  gms. 

taken  contained  9  X  0.056  =  0.504  gm.     Then 
10  gms.  :  0.504  ::  100  :  x.        x  =  5.04^. 

28  gms.  of  the  U.  S.  P.  liquor  potassa  should  require 

N 
about  25  cc.  of  the  —  acid  V.  S.,  each  cc.  representing 

®.2fc  of  KOH. 
Soda,  (NaOH  j    39*96  y  s  p.)._!  gm.  of  soda  is 

carefully  weighed,  dissolved  in  a  small  quantity  of 
water,  a  few  drops  of  phenolphthalein  added,  and  then 
titrated  with  normal  sulphuric  acid  V.  S.  until  the  red 
color  of  the  indicator  is  just  discharged.  This  equa- 
tion shows  the  reaction  : 


2NaOH  +  H,SO4  =  Na2SO4  +  H2O. 
2)80  2)98 

40  gms.  =    49  gms.  or  1000  cc.  of  —  V.  S. 

Thus  each  cc.  represents  0.040  gm.  of  NaOH.       I  gm. 

N 
should  require  22.5  cc.   of  —  acid    V.  S.,  which   indi- 


cates  ^ 

.040  X  22.5  =  .900 

.900  X  TOO 

—     -  =  90$ 

Liquor  Soda,  U.  S.  P. — This  is  an  aqueous  solution, 
containing  about  5$  of  the  hydroxide  (NaOH).  10 
grammes  of  liquor  soda  are  taken  mixed  with  a  little 
water,  a  few  drops  of  phenolphthalein  are  added,  and 

N 
then  from  a  burette  the  y  sulphuric  acid  V.  S.  in  the 


46         A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

manner  described  above.  Each  cc.  required  represents 
0.040  gm.  of  NaOH.  If  12.5  cc.  were  required,  then 
0.040  X  12.5  =  .500. 

.500  X  loo 


Aqua  Ammonise,  U.  S.  P.  —  An  aqueous  solution  of 
ammonia  (NH3  =  17.01)  containing  \Q%  by  weight  of 
the  gas. 

Three  grammes  of  ammonia  water  are  diluted  with  a 
little  water,  a  few  drops  of  rosolic  acid  T.  S.  are  added, 

N 
and  then  —  sulphuric  acid  V.  S.  slowly  from  a  burette 

until  the  yellow  color  indicates  that  all  the  alkali  is 
neutralized.  Phenolphthalein  is  not  suitable  as  an  indi- 
cator for  ammonia.  Litmus  may  be  used,  but  it  is  not 
as  delicate  an  indicator  as  rosolic  acid. 

N 
Each  cc.  of  —  acid  V.  S.  used    represents   0.017  gm. 

NH3  or  *o.O35  gm.  NH4OH,  as  shown  by  the  equation 
2NH34°H,0  }  +      H*S°<  =  (NH<)'SO<  +  2H'°' 

2NH4OH     2NH3.  H2Q      2)98 

^        ^T  49       =  to  1000  cc.  3  acid  V.  S. 

35  17  i 

N 
If  the   3  gms.  required  17.8  cc.  ~  acid  V.  S.,  then  it 

contained  17.8  X  .017  gm.  =  0.3026  gm. 


According  to  the  U.  S.  P.,  3.4  gms.  should  require  20 
cc.  of  normal  acid  V.  S. 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.         47 

Aqua  Ammonias  Fortior,  U.  S.  P.  (Stronger  Am- 
monia Water). — An  aqueous  solution  of  ammonia  (NHS) 
containing  about  28$  by  weight  of  the  gas.  This  is 
estimated  in  the  same  manner  as  aqua  ammonia,  two 
grammes  of  the  stronger  ammonia  water  being  taken 
instead  of  three. 

Spiritus  Ammoniac  (Spirit  of  Ammonia). — This  is 
an  alcoholic  solution  of  NH3,  containing  10$  by  weight 
of  the  gas. 

3.4  grammes  (or  4.2  cc.)  of  the  spirit  are  diluted  with 

N 
water  and  treated  with       sulphuric  V.  S.    Each  cc.  of 

N 
the  —  acid  solution  used  represents  .017  gm.  of  NH3 

or  0.5$.     20  cc.  should  be  required.     Rosolic  acid  is 
the  indicator. 


ESTIMATION   OF  ALKALINE   CARBONATES. 

When  carbonates  are  treated  with  acids  carbonic- 
acid  gas  is  liberated.  This  gas  shows  an  acid  reaction 
with  most  indicators,  and  the  reaction  will  seem  to  be 
completed  before  the  alkali  is  entirely  neutralized. 
To  avoid  this  the  process  is  conducted  at  a  boiling 
temperature  in  order  to  drive  off  the  COa.  The  stand- 
ard acid  being  added  until  two  minutes'  boiling  fails 
to  restore  the  color  indicating  alkalinity.  If  the  titra- 
tion  is  conducted  at  a  boiling  temperature  it  is  advisa- 
ble to  attach  to  the  lower  end  of  the  burette  a  long 
rubber  tube  with  a  pinch-cock  fixed  about  midway  on 
the  tube. 

The   boiling  can  then  be  done  at  a  little  distance 


48         A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

from  the  burette  and  the  expansion  of  the  standard 
solution  therein  thus  prevented. 

Another  and  better  method  is  to  use  methyl  orange 
as  an  indicator,  and  conduct  the  process  by  simple 
titration  without  the  use  of  heat. 

Methyl  orange  is  not  affected  by  CO2.  When 
methyl  orange  is  used  as  an  indicator,  standard  sul- 
phuric acid,  and  not  oxalic  acid,  should  be  employed. 
The  reaction  of  the  latter  with  this  indicator  is  not  very 
sharp. 

Potassium  Carbonate,  K2CO3  =  j  *II^'91-— Weigh 

carefully  one  gramme  of  the  salt,  dissolve  in  a  small 
quantity  of  water  in  a  beaker  or  flask,  add  a  few  drops 
of  methyl  orange  T.  S.,  and  titrate  with  normal  sul- 
phuric acid  until  a  faint  orange-red  color  appears. 

K2C03  +  H2S04  =  K2S04  +  H,0  +  CO2. 

2)138  2)g8_  N 

69  49      =  grammes  in  1000  cc.  —  V.  S. 

N 
Each   cc.    of  —    H2SO4,  therefore,    represents    0.069 

gramme  (more  accurately  0.068955  gramme)  of  pure 
dry  potassium  carbonate. 

Thus  if  14.4  cc.  of  the  normal  acid  were  required,  the 
salt  contained  14.4  X  .069  =  .9936  grammes  of  pure 
K2CO3,  or  99.36  per  cent.  The  U.  S.  P.  requirement 
is  that  0.69  grammes  of  the  salt  be  neutralized  by  not 
less  than  9.5  cc.  of  normal  acid,  corresponding  to  95$ 
of  the  pure  salt.* 

When  methyl  orange  is  used  the  end  reaction  is  not 
very  well  defined,  and  practice  is  required  to  obtain 
good  results.  If  it  is  desired  to  use  litmus  or  phenol- 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.         49 

phthalein,  it  will  be  necessary  to  boil  the  solution  as  de- 
scribed above. 

*.o69  X9-5  =0.6555 
0.6555  X  ioo 


Potassium    Bicarbonate,    KHCO3  =  j  #  '       •  — 

^    i  oo 

The  process  is  exactly  the  same  as  that  for  the  car- 
bonate. 

2KHC03  +  H2S04  -  K2S04  +  2H2O  +  2CO2. 
2)200  2)98  N 

ioo  49  =  to  grammes  in  1000  cc.  of  —  acid. 

N 
Each  cc.  of  —  acid  represents  o.  I  gramme  (more  ex- 

actly 0.09988  gramme)  of  pure  KHCO3. 

The  U.  S.  P.  requirement  is  that  I  gramme  of  the 
salt  be  neutralized  by  not  less  than  10  cc.  of  normal 
acid  (corresponding  to  ioo  per  cent  of  the  pure  salt). 

Sodium  Carbonate,  Na1CO,+  ioH,O=  j  #^5^-— 

Dissolve  two  grammes  of  sodium  carbonate  in  suffi- 
cient water,  add  a  few  drops  of  methyl  orange,  and 
titrate  as  described  under  potassium  carbonate. 

Na2C03  +  ioH20  +  H2S04  =  Na2SO4  +  1  1  H2O  +  CO2. 
2)286  2)98  N 

143  49  =  grammes  in  1000  cc.  —  acid  V.  S. 

N 
Each  cc.  of  —  acid  V.  S.   represents  0.143  gramme 

of  crystallized  sodium  carbonate. 


50         A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

The  U.  S.  P.  directs  that  the  salt  be  deprived  of  its 
water  of  crystallization  by  heat  immediately  before 
being  weighed,  and  that  i  gramme  of  the  anhydrous 
carbonate  should  neutralize  not  less  than  18.7  cc.  of 

N 

—  sulphuric  acid,  corresponding  to  98.9$. 

Sodium  Carbonate  (exsiccated). — Operate  upon  i 
gramme  of  the  salt  as  described. 


Na3C03  +  H2S04  =  Na2S04  +  H2O  +  CO9. 
2)106  2)98  N 

53  49  =  grammes  in  1000  cc.  —  acid. 

N 
Each  cc.  of  the  —    acid   represents  .053  gramme  of 

anhydrous  sodium  carbonate.  The  U.  S.  P.  require- 
ment is  that  not  less  than  13.8  cc.  of  normal  sulphuric 
acid  should  neutralize  i  gramme  of  the  salt,  corre- 
sponding to  about  73  per  cent  of  anhydrous  sodium 
carbonate. 

.053  X  13-8  =  7314     or     73.14^ 

Sodium  Bicarbonate,  NaHCO3  =  j  ^3'85.— Oper- 
ate upon  i  gramme  of  the  salt,  and  proceed  in  the 
usual  way. 

2NaHCOs  +  H2SO4  =  Na2SO4  +  2H2O  +  2CO,. 
2)168  2)98  N 

84  49  =  to  grammes  in  looocc.  -  acid. 

N 
Thus  each  cc.  of  —  acid  represents  .084  gramme  of 

pure  sodium  carbonate. 

According  to  the  U.  S.  P.,  0.85   gramme  of  sodium 


A    TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.          51 

bicarbonate  should  require  not  less  than  10  cc.  of  nor- 
mal sulphuric  acid,  which  corresponds  to  at  least  98.6$ 
of  the  pure  salt. 

.084  X  10  —  .84 


Lithium  Carbonate,  Li2CO3  =  j  J^*7.— 


H2S04  =  Li,S04  +  HS0  +  CO, 
2)74  2)98  N 

37  49  =  grammes  in  1000  cc.  —  acid. 

N 
Each   cc.    of   -~   acid    represents   0.037   gramme    of 

lithium  carbonate  (more  accurately  .03693).  0.5  gm. 
of  dry  lithium  carbonate  are  mixed  with  about  20 
cc.  of  water  in  a  beaker,  a  few  drops  of  methyl  orange 
T.  S.  added,  and  titration  proceeded  with  until  a  faint 
orange-red  color  of  the  solution  indicates  the  complete 
neutralization  of  the  lithium  carbonate. 

To  comply  with  the  U.  S.  P.  test,  0.5  gm.  should 
require  for  complete  neutralization  not  less  than  13.4 
cc.  of  normal  sulphuric  acid,  corresponding  to  at  least 
98.98  per  cent  of  the  pure  salt. 

0.03693  X  134  =  0.494862  gm. 

0.494862  X  IPO 

—  —  =  98.98$ 

Ammonium  Carbonate,  N3H11C2O6  =  j  ^6'77  . 
—  Normal  ammonium  carbonate  has  the  formula 


52         A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


but  the  normal  salt  loses  upon  exposure 
NH3  and  H2O.  The  commercial  salt,  therefore,  gen- 
erally is  a  mixture  of  carbamate  and  bicarbonate. 

(NH4)2CO3-  NH,=  NH4HCO3; 
(NH4)2CO3  -  H2O  =  NH4NH2CO2. 

The  commercial  carbonate  is  therefore  generally 
expressed  thus: 

NH4HCO,.NH4NH1CO,    or     N3HnC3O5- 

For  estimating  the  ammonium  carbonate  the 
U.  S.  P.  recommends  the  following  procedure:  Dis- 
solve 7.84  gms.  of  unaltered  ammonium  carbonate 
in  water  to  the  volume  of  90  cc.  Take  30  cc.  of 
this  solution  (which  contains  2.613  gms.  of  the  salt), 
add  a  few  drops  of  rosolic  acid  T.  S.,  and  titrate  with 

N 
-  H2SO4  V.  S.  until  the  violet-red  color  is  replaced  by 

N 
yellow.     50  cc.   of  the   —  H2SO4   should   be   required 

before  this  change  takes  place,  corresponding  to  loofo 
of  pure  salt. 

2N,HUCA  +  3H2S04  =  3(NH4)2S04  +  4CO2  +  2H2O. 
6)313.54  6)254  N 

52.256  49  =  to  1000  cc.  —  acid  V.  S. 

Each  cc.,  therefore,  represents  0.052256  gm.  of  am- 
monium carbonate. 

50  cc.  =  50  X  .052256  =  2.6128  gms. 

2.6128  X  ioo 

--  -,  --- 

2.613 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS,         53 

Although  rosolic  acid,  on  account  of  its  sensitiveness 
to  ammonia,  is  recommended  in  the  U.  S.  P.  process, 
yet  it  must  be  remembered  that  this  indicator  is  af- 
fected by  CO2 ,  and  therefore  great  care  should  be 
exercised  in  this  estimation.  It  must  also  be  remem- 
bered that  if  heat  is  employed  to  dispel  the  CO2  it  is 
apt  to  occasion  a  loss  of  ammonia. 

Methyl  orange  is  not  affected  by  CO2  and  might  be 
employed  in  this  case,  but  it  is  not  as  sensitive  to 
ammonia  as  rosolic  acid. 

The  method  usually  employed  by  skilled  analysts  is 
to  add  a  measured  excess  of  the  standard  acid  solu- 
tion, and  thus  convert  the  ammonium  carbonate  into 
the  less  volatile  ammonium  sulphate  ;  then  gently  boil 
to  get  rid  of  CO2,  and  titrate  back  with  a  standard 
alkaline  V.  S.  (using  litmus  as  an  indicator)  until  the 
excess  of  acid  is  neutralized.  The  quantity  of  free 
acid  is  thus  found,  which,  when  deducted  from  the 
amount  of  acid  first  added,  gives  the  quantity  which 
was  required  to  neutralize  the  ammonium  carbonate. 

Thus,    2.613  gm-    m  solution  of  ammonium  carbo- 

N 
nate  are  treated  with  70  cc.  of  —  H2SO4  V.  S.,  which  is 

more  than  sufficient  to  neutralize    it ;  the  solution  is 
then  gently  boiled  to  drive  off  COa,  a  few  drops  of 

N 
litmus  tincture  added,  and  then  titrated  with  —  KOH 

V.  S.  until  the  litmus  no  longer  shows  an  acid  reaction 
and  the  solution  is  neutraL 

N 
Let  us  assume  that  20  cc.  of  the  —  KOH  V.  S.  were 

N 
used.     By  deducting  the  20  cc.  from  the  70  cc.  of  - 


54         A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

acid  first  added  we  find  that  50  cc.  of  the  acid  went 
into  combination  with  the  ammonium  salt.  Thus, 

50  X  .052256  =  2.6128  (*2.6i3) 

2.613  X  ioo 

-  =  loofo 
2.613 

Borax,Na2B407.ioH20^|  ^o.92^_Two   gms>   of 

borax  are  dissolved  in  a  small  quantity  of  water,  a 
few  drops  of  tincture  of  litmus  are  added,  and  the 
solution  titrated  with  normal  oxalic  acid  V.  S.,  or  some 

other  —  acid  V.  S. 
i 

Boric  acid  is  liberated  during  the  operation,  which 
colors  the  litmus  wine-red.  This  is  not  regarded,  and 
the  titration  is  continued  until  the  bright  red,  due  to 
the  action  of  free  oxalic  acid,  makes  its  appearance. 
Apply  the  following  equation  : 

Na2B407.ioHaO  +  HaC2O4.2H2O 

2)382  2)126  N 

191  63  gms.  =  looo  cc.  —  V.  S. 

=  Na.C.0.  +  H.BA  +  I2H.O. 

N 

Thus  each  cc.  of  -  -  oxalic  acid  V.  S.  represents 
0.191  gm.  crystallized  borax. 


ORGANIC   SALTS   OF  THE  ALKALIES. 

The  tartrates,  citrates,  and  acetates  of  the  alkali 
metals  are  converted  by  ignition  into  carbonates,  the 
whole  of  the  base  remaining  in  the  form  of  carbonate. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         55 

Each  molecular  weight  of  a  normal  tartrate  gives 
when  ignited  one  molecular  weight  of  carbonate  : 

K.C.H.O.  =  K.CO.. 

Every  two  molecular  weights  of   an  acetate  or  an 
acid  tartrate  give  one  molecular  weight  of  carbonate  : 

2KC.H.O,  -  K,CO,  ; 
2KHC4H406  =  K,C08. 

Every  two    molecular  weights  of  a  normal  citrate 
give  three  molecular  weights  of  carbonate  : 


These  reactions  are  taken  advantage  of  in  volumet- 
ric analysis,  and  the  tartrates,  citrates,  and  acetates  of 
the  alkalies  .  are  indirectly  estimated  by  calculating 
upon  the  quantity  of  carbonate  formed  by  burning 
them,  the  quantity  of  carbonate  being  found  by  titra- 
tion  in  the  usual  manner. 

Potassium  Tartrate,  K2C4H4O6.H2O  =  j  ^2^6.- 

Two  gms.  of  the  salt  are  placed  in  a  platinum  or  por- 
celain crucible  and  heated  to  redness  in  contact  with 
the  air  until  completely  charred  ;  that  is  to  say,  until 
nothing  is  left  in  the  crucible  but  carbonate  and  free 
carbon. 

The  crucible  is  now  cooled,  and  its  contents  treated 
with  boiling  water,  which  dissolves  the  potassium  car- 
bonate, the  carbon  being  separated  by  filtration.  In 
order  to  obtain  every  trace  of  carbonate  it  is  well  to 
wash  the  crucible  with  several  small  portions  of  hot 


56         A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

water,  and  add  the  washings  to  the  rest  of  the  filtrate 
through  the  filter. 

If  the  salt  is  completely  carbonized  the  filtrate  will 
be  colorless,  but  if  the  carbonization  is  not  complete 
the  solution  will  be  more  or  less  colored,  and  should  be 
rejected,  and  a  fresh  quantity  of  the  salt  subjected  to 
ignition. 

To  the  filtrate,  which  contains  potassium  carbonate, 

N 
add  a  few  drops  of  methyl-orange,  and  titrate  with  - 

sulphuric  acid  V.  S.  until  a  light  orange-red  color 
appears  and  the  carbonate  is  neutralized. 

The  following  equations  will  explain  the  reactions : 

2(K,CLH.O..H.O)/+  50,  =  2K,CO,  +  6CO,+  6H,O  ; 

488  276 

then 

2K2CO3  +  2H2SO4  =  2K2SO4  +  2H2O  +  2CO2 ; 

276  196 

therefore 

2(K2C4H406.H20)  =  2K2C03  =  2H2S04, 

4)488  4)276  4)196  N 

122  gms.  =  69  gms.  =      49  gms.  =  1000 cc.—  V.  S., 

N 

and  each  cc.  of—  H2SO4  represents  0.122  gm.  of  po- 
tassium tartrate. 

Example. — Two  gms.  of  potassium  tartrate  treated  as 

N 
described  above  require  16.3  cc.  of  --  H2SO4  V.  S.    It 

therefore  contains  0.122  X  16.3  ==  1.9886  gms. 

1.9886  X  100 

--          =  99-43^ 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.         57 

Potassium  and  Sodium  Tartrate  (Rochelle  Salt), 
KNaC4H406.4H,0  =    j  ^•5I^TIfe  salt  is  treated 


in  exactly  the   same  way  as  described   for  potassium 
tartrate. 

When  ignited  the  double  tartrate  is  converted  into 
a  double  carbonate  of  potassium  and  sodium  : 

50, 


=  2KNaCO,  +  6CO.+  I2H2O  ; 
244 

then 

2KNaCO3  +  2H,S04  =  2KNaSO4  +  2COa  +  2H2O  ; 
244  196 

therefore 

2KNaC4H4O6.4HaO  =  2KNaCO8  =  2H,SO4  , 

4)564  4)244  4)196  N 

141  61  49  =iooocc.—  V.  S. 

N 
and    each    cc.    of   —  H2SO4  represents   0.141   gm.   of 

KNaC4H4O6.4H,0. 

The  U.  S.  P.  directs  t'hat  1.41  gms.  of  Rochelle  salt 
when  completely  decomposed  by  ignition  should  leave 
an  alkaline  residue,  which  requires  not  less  than  locc. 

N 
of—  H2SO4  for  complete  neutralization,  corresponding 

to  loofo  of  the  pure  salt. 

The  factor  is  0.141  ;    10  cc.  =  .141  X  10  =  1.41. 


1.41 


58         A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

Potassium  Bitartrate  (Cream  of  Tartar),  KHC4H4O6 

=  1  *l88       — ^e  es^mat^on  °f  this  salt  is  affected  in 
the  same  way  as  the  tartrate. 

The  bitartrate  having  but  one  atom  of  potassium  in 
its  molecule,  it  takes  two  molecules  to  form  one  mole- 
cule of  carbonate. 


2KHC4H406  +  502  =  K2C03  +  ;C02 

376  138 


then 


K2C08  +  H2S04  =  K2S04  +  H20  -f  COa ; 

138  98 


therefore 

2KHC4H4O6  =  K2C03  =  H2S04 , 

2)376  2)138  2)98  N 

188  69  49  =1000  cc.  of  —  V.  S. 

and  each  cc.  of  —  H2SO4  V.  S.  =  0.188  gm.  of  KHC4 

H40, 

Another  way  of  estimating  bitartrate  is  to  dissolve  a 

N 

weighed  quantity  in  hot  water  and  titrate  with  —  po- 
tassium hydrate  until  neutral,  and  thus  the  amount  of 
tartaric  acid  existing  as  bitartrate  is  found.  The  bitar- 
trate is  always  acid  in  reaction.  This  latter  is  the  U. 
S.  P.  method.  In  detail  it  is  as  follows: 

1.88  gms.  of  the  bitartrate  are  dissolved  in  100  cc.  of 
hot  water,  a  few  drops  of  phenolphthalein  T.  S.  added, 

N 
and  then  titrated  with  —  KOH  V.  S.  until  a  faint  pink 

color  indicates  that  all  of  the  acid  has  been  neutralized. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.         59 

Not  less  than  9.9  cc.  of  the  normal  alkali  should  be  re- 
quired, corresponding  to  99$  of  pure  salt. 

The  following  equation  will  show  the  reaction  : 

KHC4H406  +  KOH  =  K2C4H406  +  H2O. 

188  56  =  1000  cc.  of  *?  KOH  V.  S. 

i 

Each  cc.of  y  KOH  V.  S.  represents  .188  gm.  of  KH 

C4H406. 

If  9.9  cc.  are  required  for  neutralization,  then  9.9  X 
.188=  1.  8612  gms. 

i.  8612  X  ioo 


Lithium     Citrate,      Li3C6H6O7  =  |  ^oo,57._This 

salt  is  estimated  in  the  same  way  as  the  other  organic 
salts. 

I  gm.  of  the  salt  is  thoroughly  ignited   in  a  porce- 
lain crucible,  and  the  resulting  lithium  carbonate  mixed 

N 
with  20  cc.  of  water  and   titrated  with  —  H2SO4  V.  S. 

after  having  added  a  few  drops  of  methyl-orange  T.  S. 

N 
Each  cc.  of  the  —  V.  S.  used  before  neutralization   is 

effected   represents   ,070  gm.  of  pure   lithium   citrate. 
The  U.  S.  P.  salt  requires  not  less  than   14.2  cc.  of  the 

'-''"':: 


The  following  are  the  reactions: 
2Li,C.HsO,  +  90,  =  3Li,COs  +  5H,0  +  9CO,  ; 

420  222 


60         A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

then 

3Li2C03  +  3H,S04  -  3Li2S04  +  3H20  +  3CO2  ; 

222  294 

therefore 

2Li3C6H607  =  3Li2C03  =  3H2S04 

6)420  6)222  6)294 

70  gms.  37  gms.  49  gms.  =rooo  cc. 

of  the  —  sulphuric  acid  V.  S.,  and  thus  each  cc.  of  — 

H3SO4  V.  S.  =  .070  gm.  of  the  pure  lithium  citrate. 

If  14.2  cc.  of  the  normal  acid  are  required,  then  I 
gm.  of  the  salt  contains  .070  X  14.2  =  .994  gm.,  or 
99.4$.  If  the  more  accurate  factor  .069856  is  used, 
the  per  cent  will  be  99.2. 

Potassium  Citrate,  K,C.H6O7.HaO  j  ^323-59.— TWO 

gms.  of  the  salt  are  placed  in  a  platinum  or  porcelain 
crucible  and  thoroughly  ignited  at  a  red  heat  in  con- 
tact witli  air. 

The  potassium  citrate  is  thus  converted  into  potas- 
sium carbonate,  carbon,  and  gases.  When  the  crucible 
is  cool,  hot  water  is  added  to  its  contents,  and  the  solu- 
tion of  potassium  carbonate  thus  obtained  is  filtered 
to  separate  the  carbon.  To  the  solution,  which  must 
be  colorless,  add  a  few  drops  of  methyl-orange  T.  S., 

N 
and  titrate  with  —  H2SO4  V.  S.  until  the  change  of  color 

indicates   complete    neutralization.       Each   cc.   of   the 

N 
-   HaSO4    required    before    neutralization    is    effected 

represents  0.108  gm.  of  the  pure  salt. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.         6l 

2(K.C.H.O,.H.O)  +  90,  =  3K,CO,  +  3CO,  +  7H,O  ; 

648  414 

then 

3K,CO,  +  3H,SO.  =  3K,S04  +  3  CO,  +  3H5O ; 

414  294 

therefore 

2K3C6H6O7-H2O  =  3K2CO3=  3HaSO4. 

6)648  6)414  6)294  N 

108  gms.  69  gms.          49  gms.  =  1000  cc.  —  acid. 

N 
Thus  each  cc,  of  --  acid    represents  0.108   gm.    of 

pure  potassium  citrate. 

The  U.  S.  P.  directs  that  1.080  gms.  of  potassium 
citrate  be  thoroughly  ignited  at  a  red  heat,  and  that 
the  alkaline  residue  should  require  for  complete  neutra- 

N 

lization  not  less  than  10  cc.  of  —  H2SO4  V.  S.  (corre- 
sponding to  100$  of  the  pure  salt),  using  methyl-orange 
as  indicator. 

The  factor,  as  has  been  shown,  is  o.  108  for  potassium 
citrate. 

.108  X  10=  1.08 
1.08  X  ioo 

-Tbir    --100* 

Potassium  Acetate,  KC2H3O,  =  j  ,97-89  __In  esti. 

mating  potassium  acetate  the  salt  is  ignited  and  the 
residue  treated  in  exactly  the  same  manner  as  in  the 
estimation  of  the  citrates  and  tartrates  before  men- 


62         A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

tioned.  According  to  the  U.  S.  P.,  "  if  I  gm.  of  potas- 
sium acetate  be  by  thorough  ignition  converted  into 
carbonate,  the  residue  should  require  for  complete 

N 
neutralization   not  less  than   10  cc.  of  —  H2SO4  V.  S. 

(corresponding  to  at  least  98  per  cent  of  pure  potas- 
sium acetate),  methyl-orange  being  used  as  indicator." 

2KC.H.O.  +  40,  =  K,COS  +  3H,0  +  3CO, : 

196  138 

then 

K2CO3  +  H2S04  =  K2S04  +  HaO  -f-  CO, ; 

138  98 

therefore 

2KC2H302  =  K2C03  =  H2S04. 

2)196  2)138  2)98  N 

98  gms.  69  gms.         49  gms.  =  1000  cc.  ~'  H2SO4 . 

N 
Each  cc.  therefore  of  —  H2SO4  V.  S.  corresponds  to 

.098  gm.  of  potassium  acetate. 

If  IO  cc.  are  required  to  neutralize  the  residue  from 
I  gm.  of  potassium  acetate,  the  salt  contains  10  X  -098 
=  0.98  gm.,  or  T9Q8^  of  I  gm.,  which  is 


Sodium  Acetate,  NaC2H3O2.3H2O  =  {  #Jf|'74 "- 

This  salt  is  estimated  in  the  same  manner  as  the  potas- 
sium acetate  U.  S.  P.  1.36  gm.  of  the  salt  is  ignited 
until  completely  carbonized,  the  residue  is  treated 
with  hot  water,  the  solution  thus  obtained  is  filtered, 
and  to  the  filtrate  a  few  drops  of  methyl-orange  T.  S. 

N 
are  added,  and  then  the  —  sulphuric  acid  until  neutra- 


A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.         63 

lization  is  effected.     10  cc.  of  the  latter  should  be  re- 
quired. 

2(NaCaH30, .  3HaO)  +  40,  =  Na,CO3+  9HaO 

272  106 


then 


NaaCO3  +  HaS04  =  NaaSO4  +  HaO  +  COa ; 

106  98 


therefore 

2(NaC3H302  .3HU0)  =  NaaCO3=H2SO4. 
2)272      •  2)106          2)98 

136  gms.  53  gms.       49  gms., 

or  1000  cc.  —  H2SO4. 

Each   cc.   therefore    represents  0.136   gm.   of   sodium 
acetate. 

N 
If  10  cc.  of  the  —  acid  are  required  to  neutralize, 

multiply  the  factor  0.136  gm.  by  10  =  1.36  gms. 
1.36  X  ioo 


Lithium  Benzoate,  LiC7HBOa  j  *"7'72.—  This  salt 

when  ignited  chars,  emits  inflammable  vapors  having 
a  benzoin-like  odor,  and  finally  leaves  a  residue  of 
lithium  carbonate  mixed  with  free  carbon.  It  may 
therefore  be  estimated  in  the  same  manner  as  are  the 
citrates,  tartrates,  and  acetates. 

One  gm.  of  the  salt  is  placed  in  a  porcelain  crucible  and 
thoroughly  ignited.  The  resulting  residue,  consisting 
of  lithium  carbonate  and  free  carbon,  is  then  mixed  with 


64         A   TEXT-BOOK   OF  VOLUiMETRIC   ANALYSIS. 

about  20  cc.  of  water  and  a  few  drops  of  methyl-orange. 

N 
The   titration  is  then    begun,  and  each  cc.  of  the  - 

H2SO4  V.  S.  used  represents  about  0.128  gm.  of  pure 
lithium  benzoate.  The  U.  S.  P.  requires  the  salt  to  be 
99.6^. 

The  reactions  are  expressed  as  follows : 

2LiC;HA+  I502  =  Li2C03  -f  5H20  +  i3C02 ; 

256  74 

then 

Li2C03  +  H2S04  =  Li2S04  +  H20  +  CO, ; 

74  98 

therefore 

2LiC7H602  =  Li2C03  =  H2SO4. 

2)256  2)74  2)98  N 

128  gms.  37  gms.          49  gms.  or  1000  cc.  —  H2SO4. 

N 
If  7.8  cc.  of  —   H2SO4  V.  S.  are  used  to  neutralize 

the  residue  from  the  ignition  of  the  lithium  benzoate", 
then 

.128  X  7-8  =  .9984  gm. ;     then     '"  4y        -  =  99.84$ 


Sodium  Benzoate,  NaC7HBO2  =     *,-— Jgnite 

2  gms.  of  the  salt  in  a  porcelain  crucible  until  com- 
pletely carbonized.  Dissolve  the  residue  in  about  20 
cc  of  hot  water,  filter  the  solution,  rinse  the  crucible 
with  a  little  water,  and  add  it  through  the  filter  to  the 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.         65 

first  filtrate.     Then  add  a  few  drops  of  methyl-orange 

N 
T.  S.  and  titrate  with  —  H2SO4  until  neutralization  is 

effected,  as  shown  by  the  indicator.     It  should  require 

N 

not  less  than  13.9  cc.  of  the  —  H2SO4  V.  S.,  which  cor- 
responds to  99.8^0  of  pure  salt. 
The  following  are  the  reactions : 

2NaC,Hs05  +  iS0.  =  Na,C03  +  5H,O  +  I3CO,; 

288  106 


then 


Na2C03  +  H2SO4  =  Na2S04  +  H2O  +  CO, 

106  98 


therefore 


2NaC7HBOa  =  Na2CO3  =  H2SO4. 

2)288  2)106  2)98  N 

144  gms.  53  gms.        49gms.  or  looocc.  —  H2SO4  V.  S. 

N 
Each  cc.  of  —  H2SO4  V.  S.  therefore  represents  0.144 

gm.  of  sodium  benzoate,  or  more  accurately  0.14371. 

If   13.9  cc.  are   required,  then   the   2    gms.  contain 
0.14371  X  13-9=  i -997  569- 

1-997569x100    _.nabout 


The  salicylates  of  the  alkalies  are  estimated  in  the 
same  way  as  are  the  benzoates,  tartrates,  etc. 


66         A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

Lithium  Salicylate,  LiC7H5O3  =  j  ^6S.— Lith- 
ium salicylate  when  heated  is  decomposed,  an  odor  of 
phenol  is  emitted,  and  a  residue  of  lithium  carbonate 
and  carbon  is  left.  It  may  therefore  be  estimated  as 
are  benzoates,  tartrates,  citrates,  etc. 

The  process  is  as  follows : 

Two  gms.  of  the  salt  are  ignited  in  a  porcelain  crucible, 
so  as  to  convert  it  into  carbonate.  This  carbonate  is 
mixed  with  about  20  cc.  of  hot  water,  a  few  drops  of 
methyl-orange  T.  S.  added,  and  then  titrated  with 

N 

—  H2SO4   until   neutralized.      Not  less  than    13.8  cc. 

should  be  required,  each  cc.  representing  0.14368  gm. 
of  the  pure  salt. 
The  reactions  are: 


2LiC7H603  +  i402  =  Li2C03  +  5H20+  i3C02 ; 

287.36  74 


then 


Li2CO,  +  H2S04  =  Li2S04  +  H20  +  CO, ; 

74  98 


therefore 


2LiC7H5O3  =  UCO3  =  HaSO4. 

2)287.36  2)74  2)98  N 

143.68  gms.  37  gms.          49  gms.  or  1000  cc.  —  acid. 


N 
Each  cc.  of  —   H2SO4  therefore  represents  0.14368 

gm.  of  lithium  salicylate. 


A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.         67 

N 

If  13.8  cc.  of  —   H2SO4  are  required  for  neutraliza- 
tion, then  .14368  X  13.8  =  1.982784. 

1.982  X  ioo 

-  =  99.13$. 


Sodium   Salicylate,   NaC,H5O,  ±=  |  *j^67.— This 

salt,  when  heated,  is  decomposed,  inflammable  vapors 
and  an  odor  of  phenol  being  given  off,  and  a  residue  of 
sodium  carbonate  and  free  carbon  being  left. 

No  volumetric  process  is  given  in  the  U.  S.  P.  for 
the  estimation  of  this  salt.  The  foregoing  processes, 
however,  may  be  applied  to  it,  the  alkaline  carbonate 
which  is  left  being  titrated  with  sulphuric  acid  V.  S., 

N 
each  cc.  of    —  H2SO4  V.  S.  representing  0.15967  gm., 

or  approximately  o.  160  gm.,  of  the  pure  salicylate. 


2NaC7H503  +  I403  =  Na2C03  +  5H2O  +  i3COa; 

319.34  106 


then 


Na.CC>,  +  H2S04  =  Na2S04  +  H2O  +  CO, 

1 06  98 


therefore 


2NaC7H503  =±  Na,CO,  =  H,SO4. 

2)319.34  2)106  2)98 

159.67  gms.  53  gms.          49  gms.  or  IOQO  cc. 


68         A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


TABLE  SHOWING   THE    APPROXIMATE  NORMAL   FACTORS,   ETC.,  OF 
THE  ORGANIC  SALTS  OF  THE  ALKALINE  METALS. 


Substance. 

Formula. 

Molecular 
Weight. 

Equivalent 
Weight  in 
Carbonate. 

Normal 
Factor.* 

Lithium  benzoate.  ...      .  .  . 

LiC7HBO2 

128 

07 

O   1  28 

"        citrate  

Li3C6H6O7 

2IO 

III 

O  O~O 

"        salicylate    .... 

LiC7H5O3 

IAA. 

Sodium  acetate  
"        benzoate  

NaC2H3O2.3H2O 
NaC7H5Oa 

136 
Idd. 

o/ 
53 

e  -3 

0.136 
O    1.1-1 

"       salicvlate  

NaC7H5O3 

1  60 

C  0 

o  1  60 

Potassium  acetate 

KC,HtOi 

08 

60 

bitartrate  
"           citrate 

KHC«H4Oj 

K3CfHBO7  H2O 

v° 

188 

69 

0.188 

o  1  08 

tartrate  

K2C<H4O6  H2O 

J-^4 

2AA 

1^8 

O    1  22 

and  scdii  :n   tar- 
trate 

KNaC4H4O6  4H2O 

282 

*  This  is  the  coefficient  by  which  the  number  of  cc.  of  normal  solu- 
tion used  is  to  be  multiplied  in  order  to  obtain  the  quantity  of  pure 
substance  present  in  the  material  examined. 


ACIDIMETRY. — ESTIMATION  OF  ACIDS  BY  NEUTRALI- 
ZATION. 

In  the  previous  experiments  it  has  been  shown  how 
alkalies  are  estimated  by  the  use  of  acid  solutions  of 
known  neutralizing  power.  In  the  estimation  of  acids, 
which  will  now  be  described,  the  order  is  reversed,  al- 
kaline solutions  of  known  power  being  used  in  deter- 
mining the  strength  of  acids. 

Either  an  alkaline  carbonate  or  an  alkaline  hydrox- 
ide may  be  used  in  the  form  of  standard  solution  for 
this  purpose. 

The  hydroxide,  however,  is  to  be  preferred,  for  the 
carbonate  when  used  for  titrating  an  acid  gives  off  car- 
bonic-acid gas  (CO2),  which  interferes  to  a  great  extent 
with  the  indicators. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         69 

In  the  U.  S.  P.,  1890,  volumetric  solutions  of  both 
potassium  and  sodium  hydroxides  are  official.  The 
former,  however,  is  preferable,  because  it  attacks  glass 
more  slowly  and  less  energetically,  and  also  foams  much 
less  than  does  the  sodium  hydroxide.  The  neutralizing 
power  of  each  is,  however,  the  same. 

The  caustic  alkalies  and  their  solutions  are  very 
prone  to  absorb  carbon  dioxide  from  the  atmosphere. 
Therefore  the  solutions  often  contain  some  carbonates, 
the  presence  of  which  will  occasion  errors  when  used 
with  most  indicators,  especially  litmus  and  phenolph- 
thalein.  Hence  when  these  indicators  or  others  which 
are  affected  by  carbon  dioxide  are  used  gentle  heat 
should  be  employed  toward  the  close  of  each  titration 
to  drive  off  the  liberated  gas. 

The  standard  solutions  of  alkaline  hydroxides  should 
always  be  preserved  in  small  vials  provided  with  well- 
fitting  cork  or  rubber  stoppers. 

In  order  to  keep  solutions  of  this  kind  special  ves- 
sels have  been  devised  (see  Fig.  22).  The  bottle  is 
provided  with  a  well-fitting  rubber  stopper  through 
which  a  tube  passes,  which  is  filled  with  a  mixture  of 
soda  and  lime,  which  absorbs  COa  and  prevents  its  ac- 
cess to  the  solution. 

An  improvement  upon  this  is  shown  in  Fig.  23,  since 
it  allows  of  the  burette  being  filled  without  removing 
the  stopper,  and  consequently  without  any  access  of 
CO2  whatever. 

Preparation  of  Normal  Potassium  Hydroxide  Vol- 
umetric Solution,  KOH  =  j  ^5-99  contains  55-99  I 

gms.  in  i  litre. — Potassium  hydroxide  is  so  prone  to  ab- 
sorb  carbon   dioxide  that  the   pure   substance   is  not 


7O       .  A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

readily  obtained  in  commerce.  If  pure  potassa  were 
easily  obtained  it  would  only  be  necessary  to  dissolve 
56  gms.  in  sufficient  water  to  make  a  litre.  But  since 
it  always  contains  some  CO2  and  H2O,  it  is  necessary 


FIG.  22, 


FIG,  23. 


to  take  a  slight  excess  and  dilute  the  solution  to  the 
proper  volume  after  having  determined  its  strength. 

The  U.  S.  P.  process  is  as  follows :  Dissolve  75  gms. 
of  potassa  in  sufficient  water  to  make  about  1050  cc.  at 
I5°  C-  (59°  F-)>  and  fiU  a  burette  with  a  portion  of  this 
solution. 

Dissolve  0.63  gm.  of  pure  oxalic  acid  in  about  10  cc. 
of  water  in  a  beaker  or  flask,  add  a  few  drops  of  phe- 
nolphthalein  T.  S.,  and  then  carefully  add  from  the 


A  TEXT-BOOK   OF    VOLUMETRIC    ANALYSIS.         71 

burette  the  potassium-hydroxide  solution,  agitating 
frequently  and  regulating  the  flow  to  drops  towards 
the  end  of  the  operation  until  a  permanent  pale-pink 
color  is  obtained.  Note  the  number  of  cc.  of  the  po- 
tassa  solution  consumed,  and  then  dilute  the  remainder 
so  that  exactly  10  cc.  of  the  diluted  liquid  will  be  re- 
quired to  neutralize  0.63  gm.  of  oxalic  acid.  Instead 
of  weighing  off  0.63  gm.  of  the  acid,  10  cc.  of  its  nor- 
mal solution  may  be  used. 

Example. — Assuming  that  8  cc.  of  the  stronger  po- 
tassa  solution  had  been  consumed  in  the  trial,  then 
each  8  cc.  must  be  diluted  to  10  cc.,  or  the  whole  of 
the  remaining  solution  in  the  same  proportion.  Thus 
if  8  cc.  must  be  diluted  to  10  cc.,  1000  cc.  must  be  di- 
luted to  1250  cc. 

8  :  10  : :  1000  :  x     x  —  1250  cc. 

It  is  always  advisable  to  make  another  trial  after 
diluting.  10  cc.  should  then  neutralize  0.63  gm.  of 
pure  oxalic  acid. 

Centinormal  Potassium  Hydroxide  V.  S.,  KOH 
=  {  ^5-99  contains  j  0-5599  gn-  in  ,  litre._This  is 

made  by  diluting  10  cc.  of  the  normal  solution  with 
enough  distilled  water  to  make  1000  cc. 

Normal    Sodium    Hydroxide    V.    S.,    NaOH  — 

{  *£96  C°ntainS  40  ^  I-:  }  '"  '  litre-Dissolve  54 
gms.  of  sodium  hydroxide  in  enough  water  to  make 
about  1050  cc.  at  15°  C.  (59°  F.),  and  fill  a  burette  with 
a  portion  of  this  solution. 

Dissolve  0.63  gm.  of  pure  oxalic  acid  in  about  10  cc. 
of  water  in  a  flask  or  beaker,  add  a  few  drops  of  phe- 
nolphthalein  T.  S.,  and  then  carefully  add  from  a  burette 


72         A   TEXT-BOOK   OF  VOLUMETRIC    ANALYSIS. 

the  soda  solution,  agitating  the   flask  or   beaker  fre- 

N 

quently,  as  directed  under  —  KOH  V.  S.,  until  a  per- 
manent pale-pink  color  is  produced.  Note  the  number 
of  cc.  of  soda  solution  consumed,  and  then  dilute  the 
remainder  of  the  solution  so  that  exactly  10  cc.  will  be 
required  to  neutralize  0.63  gm.  of  pure  oxalic  acid. 

Example.  —  If  8  cc.  of  the  stronger  soda  solution 
had  been  consumed  in  the  trial,  then  each  8  cc.  must 
be  diluted  to  10  cc.,  or  the  whole  of  the  remaining  so- 
lution in  the  same  proportion.  Thus  if  980  cc.  should 
be  still  remaining,  this  must  be  diluted  with  water  to 
make  1225  cc. 

Now  make  a  new  trial  with  the  diluted  solution  to 
see  whether  10  cc.  will  be  required  to  neutralize  0.63 

N 
gm.  of  oxalic  acid  (or  10  cc.  of  —  oxalic  acid  V..  S.). 

The   neutralizing  power  of  this  solution  is  exactly 

N 
the  same  as  that  of  —  potassium  hydroxide  V.  S.,  and 

may  be  employed  in  place  of  the  latter,  volume  for 
volume. 

The  following  acids  may  be  tested  with  either  01 
these  alkaline  solutions  :  I 

Acidum  aceticum. 

dilutum. 

"  "  glaciale. 

"         citricum. 

"         hydrobromicum  dilutum. 
"         hydrochloricum. 
"  "  dilutum. 

hypophosphorosum  dilutum, 
"         lacticum. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.         73 

Acidum  nitricum. 

dilutum. 
"         phosphoricum. 

dilutum. 

"         sulphuricum. 
"  "  aromaticum. 

dilutum. 
"         tartaricum. 

Acidum    Aceticum,   HC2H3O2  =    |  JJ&*6.  --  The 

U.  S.  P.  acetic  acid  contains  36$,  by  weight,  of  absolute 
HC,H,Oa  and  64$  of  water. 

Mix  3  gms.  of  the  acid  with  a  small  quantity  of 
water,  add  a  few  drops  of  phenolphthalein  T.  S.,  and 
titrate  with  normal  potassium  hydroxide  V.  S.  until  a 
permanent  pale-pink  color  is  obtained,  and  apply  the 
following  equation  : 

HC,H,04  +  KOH  =  KC2H303  +  H,O. 

60  56 

N 
Thus  56  gms.  or  looocc.of  —  KOH  V.  S.  will  neutral- 

ize  60   gms.    of   acetic    acid  ;     therefore    each    cc.    of 

N 

Y  KOH  V.  S.  represents  .060  gm.  of  acetic  acid. 

If  1  8  cc.  are  required  to  neutralize  3  gms.  of  the  acid, 
it  contains  18  X  .060  =  1.08  gms.  of  absolute  acetic 
acid. 

1.  08  X  100 


According  to  the  U.  S.  P.,  6  gms.  of  the  acid  should  re- 

N 
quire  36  cc.  of  y  KOH  V.  S.  for  complete  neutraliza- 

tion. 


74         A  TEXT-BOOK   OF    VOLUMETRIC   ANALYSIS. 

Acidum  Aceticum  Dilutum.— A  solution  contain- 
ing 6$,  by  weight,  of  absolute  acetic  acid. 

The  estimation  is  conducted  exactly  as  the  above. 
The  diluted  acetic  acid  U.  S.  P.  should  contain  6$  of 
absolute  acid.  24  gms.  should  require  24  cc.  of 

*  KOH  V.  S. 

24  X  .060  =  1.440 
1.440  X  IPO  ^  £g 
24 

Vinegar. — Vinegar  is  impure  diluted  acetic  acid. 
Its  strength  may  be  estimated  in  the  same  manner  as 
acetic  acid.  Phenolphthalein  must  be  used  as  an  indi- 
cator. Litmus  will  give  only  approximate  results,  be- 
cause potassium  and  sodium  acetate  both  have  a  slightly 
alkaline  reaction  with  litmus,  but  show  no  reaction 
with  phenolphthalein.*  The  absence  of  mineral  acids 
must  be  assured  before  the  volumetric  test  is  applied. 

The  strength  of  vinegar  may  also  be  estimated  by 
distilling  1 10  cc.  until  100  cc.  come  over.  The  100  cc. 
will  contain  80$  of  the  whole  acetic  acid  present  in  the 
1 10  cc.,  and  may  be  titrated  ;  or  the  specific  gravity  of 
the  distillate  may  be  taken,  and,  by  consulting  the  table 
below,  the  per  cent  strength  of  the  distillate  found. 
By  adding  20$  to  this  the  strength  of  the  original 
vinegar  is  obtained. 

Vinegar  usually  contains  from  3$  to  6f0  of  acetic  acid. 


*  Even  dark-colored  vinegar  may  be  titrated  in  this  way  when 
diluted.  If  the  color,  however,  is  too  dark,  litmus-paper  or  phenol- 
phthalein  paper  may  be  used  by  bringing  a  drop  of  the  liquid  in  con- 
tact with  the  paper  from  time  to  time  during  the  titration. 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 


75 


ACETIC  ACID   TABLE. 


Per  cent 

Per  cent 

Per  cent 

of 

Absolute 

Specific  Gravity 

of 
Absolute 

Specific  Gravity 
af.  J  15°  C. 

of 
Absolute 

Specific  Gravity 

Acetic 

at  1  59°  F. 

Acetic 

j  59°  F. 

Acetic 

at  j  59°  p. 

Acid. 

Acid. 

Acid. 

I 

I.OOO7 

26 

.0363 

51 

1.0623 

2 

I.OO22 

27 

•0375 

52 

1.0631 

3 

1.0037 

28 

.0388 

53 

1.0638 

4 

I.OO52 

29 

.0400 

54 

1.0646 

5 

1.0067 

30 

.0412 

55 

1.0653 

6 

1.0083 

31 

.0424 

56 

I.  0660 

7 

I.OOgS 

32 

.0436 

57 

1.0666 

8 

I.OII3 

33 

.0447 

58 

1.0673 

9 

I.OI27 

34 

•0459 

59 

1.0679 

10 

I.OI42 

35 

.0470 

60 

1.0685 

ii 

I.OI57 

36 

.0481 

61 

1.0691 

12 

I.OI7I 

37 

.0492 

62 

1.0697 

13 

I.OI85 

38 

.O5O2 

63 

1.0702 

14 

I.O2OO 

39 

•0513 

64 

1.0707 

15 

I.O2I4 

40 

.0523 

65 

1.0712 

16 

1.0228 

41 

•0533 

66 

1.0717 

17 

1.0242 

42 

•0543 

67 

I.072I 

18 

I.O256 

43 

.0552 

68 

1.0725 

19 

I.O27O 

44 

.0562 

69 

1.0729 

20 

1.0284 

45 

.0571 

70 

1-0733 

21 

1.0298 

46 

.0580 

1.0737 

22 

I.03II 

47 

.0589 

72 

1.0740 

23 

1.0324 

48 

.0598 

73 

1.0742 

24 

1-0337 

49 

.0607 

74 

1.0744 

25 

1.0350 

50 

.0615 

75 

1.0746 

ESTIMATION   OF  FREE    MINERAL    ACIDS   IN    VINEGAR. 

Mr.  Hehner  has  devised  the  method  given  below, 
which  has  the  merit  of  being  speedy,  scientific,  and 
accurate. 

The  method  is  based  upon  the  fact  that  acetates  of 
the  alkalies  are  always  present  in  commercial  vinegar, 
and  when  vinegar  is  evaporated  to  dryness,  and  the  ash 
ignited,  the  acetates  of  the  alkalies  are  converted 
into  carbonates.  If  the  ash  has  an  alkaline  reaction  no 
free  mineral  acid  is  present.  If,  however,  the  ash  is 


76         A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

neutral  or  acid  some  free  mineral  acid  must  be  present. 
The  quantitative  process  in  detail  is  as  follows  :  50  cc. 

N 
of  vinegar  are  mixed  with  25  cc.  of  —  soda    or   potash 

V.  S.  The  liquid  is  evaporated  to  dryness  on  a  water- 
bath,  and  the  residue  carefully  incinerated  at  the  low- 
est possible  temperature,  to  convert  the  acetates  into 

N 

carbonates.    When  cooled,  25  cc.  of         sulphuric    acid 

10 

V.  S.  are  added,  the  mixture  heated  to  expel  CO,  and 
filtered.  The  filter  is  washed  with  hot  water,  phenol- 
phthalein  T.  S.  added,  and  the  filtrate  and  washings 

N  N 

carefully  titrated  with   --  alkali.     Each.  cc.  of  —  alkali 

10  10 

used  represents  0.0049  gm.  H2SO4  or  0.003637  gm.  HC1. 

Acidum  Aceticum  Glaciale.—  Three  grns.  of  glacial 

acetic  acid  are  mixed  with  a  small  quantity  of  water,  a 

few  drops  of  phenolphthalein  T.  S.  added,  and  the  solu- 

N 
tion   titrated  with  —  potassium   hydroxide  V.  S.  until 

a  very  pale  pink  color  appears.  Each  cc.  represents 
.06  gm.  of  absolute  acetic  acid. 

49.5  cc.  are  required  by  3  gms.  of  the  U.  S.  P.  acid. 

49.5  X  .06  =  2.970  gms. 
2.970  X  IPO  = 
3 

Acidum    Citricum,    H3C6H6O7.H2O  =    j  ^'S.- 


3.5   gms.   of   citric    acid   are    dissolved    in   a   sufficient 
quantity  of  water,  a  few  drops  of  phenolphthalein  added, 

N 
and  the  solution  titrated  with  —  potassium    hydroxide 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         77 

V.  S.  until  a  very  pale  pink  color  appears.     Each  cc.  of 

N 

L  potassium  hydroxide  consumed  before  neutralization 

is  effected   represents  .070  gm.  of  the  pure  acid,  and 
50  cc.  should  be  required. 

The  reaction  is  expressed  by  the  following  equation: 

=  K3C6H507  +  4H30. 


3)210  3)168 

70  56 

Thus  56  gms,  of  KOH  or  1000  cc.  of  its  normal  solu- 
tion represent  70  gms.  of  pure  crystallized  acid,  and 
each  cc.  represents  .070  gm.  Therefore 

50  X  .070  =3.5  gms. 


Lime-juice  or  Lemon-juice,  the  chief  constituent 
of  which  is  citric  acid,  may  be  estimated  by  titrating 

N 
with  —  potassium  hydroxide  V.  S.  in  the  same  manner 

as  other  acid  solutions. 

Lime-juice  contains  on  an  average  7.84$,  rarely  as 
much  as  io#,  and  very  seldom  as  little  as  7$  of  citric 
acid. 

Commercial  lime-juice  frequently  contains  sulphuric, 
hydrochloric,  or  tartaric  acid.  Therefore  before  apply- 
ing this  test  the  absence  of  notable  quantities  of  these 
acids  must  be  insured  by  qualitative  tests. 

Acidum  Hydrobromicum  Dilutum  (Diluted  Hydro- 

bromic  Acid),  HBr  =  j  ^a76.—  A  liquid  containing  10 


78         A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

per  cent,  of  pure  hydrobromic  acid  (HBr)  and  90  per 
cent,  of  water. 

8.1  gms.  of  the  acid  are  diluted  with  a  small  quan- 
tity of   water,  a   few  drops   of   phenolphthalein  T.  S. 

N 
added,  and  then  —  potassium  hydroxide  V.  S.  added 

from  a  burette,   until  a  very  faint  pink  color  is  pro- 

N 

duced.  Note  the  quantity  of  —  alkali  used,  and  mul- 
tiply this  by  the  factor  .081  gm.  to  obtain  the  weight 
of  HBr  in  the  diluted  acid  taken. 

The  reaction  is  expressed  by  the  following  equation  : 

HBr  +  KOH  =  KBr  +  H2O. 

N 
81  gms.      56  gms.  =  1000  cc.  of  —  V.  S. 

Each  cc.  therefore  represents  .081  gm.,  or  I  per  cent, 
of  HBr. 

If  this  acid  is  made  with  tartaric  acid  and  potassium 
bromide,  a  white,  crystalline  precipitate  will  be  pro- 

N 
duced    upon  the   addition    of  the    —   alkali,  some    of 

which  will  be  neutralized  by  the  dissolved  potassium 
bitartrate  and  the  excess  of  tartaric  acid,  and  an  incor- 
rect indication  will  be  given. 

Acidum  Hydrochloricum  (Muriatic  Acid),  HC1  — 

)  *^64     — ^   li*!11^    containing    31.9   per    cent.,  by 

weight,  of  absolute  HC1  and  68.1  per  cent,  of  water. 

3  gms.  of  hydrochloric  acid  are  diluted  with  a  little 
water,  a  few  drops  of  phenolphthalein  added,  and  then 

N 
-  potassium  hydroxide  V.  S.  from  a  burette,  until  a 


A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.         /Q 

N 
faint  pink  color  is  produced.     Note  the  quantity  of  - 

alkali  used,  and  apply  the  following  equation : 
HC1  +  KOH  =  KC1  +  H30. 

36.4  gms.     56  gms.  =     1000  cc.  —  V.  S. 


N 

Each  cc.  of  —  alkali  required  before  the  acid  is  neu- 
tralized represents  .0364  gm.  of  pure  HC1. 

3.64  gms.  of  the  U.S. P.  acid  should  require  for  com- 

N 
plete  neutralization  31.9  cc.  of  —  KOH  V.  S. 

Diluted  hydrochloric  acid,  U.  S.  P.,  contains  10  per 
cent,  of  absolute  HC1.     3.64  gms.  of  the  diluted  acid 

N 
should   require   for   neutralization    10  cc.  of  —    KOH 

V.  S. 

Let  us  assume  that  the  3  gms.  of  hydrochloric  acid 

required  20  cc.  of  -  KOH  V.  S.     Then 

20  X  .0364  =  .7280  gm. 
of  pure  HC1  in  3  gms.  of  the  acid. 

.7280  X  ioo 

-y-     -  =  24.26^ 

Acidum    Hypophosphorosum    Dilutum    (Diluted 
Hypophosphorous  Acid). — The  U.  S.  P.  acid  contains  10 

per  cent,  of  absolute  HPH8O2  =  j  **j|'88. 


80        A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

This  acid  is  estimated  in  exactly  the  same  way  as 
the  acids  previously  noticed  :  * 

HPHa03  +  KOH  =  KPH.O.  +  H2O. 

66  gms.  =       56  gms.  =     1000  cc.  —  alkali. 

N 
Thus   each   cc.    of   —    alkali   represents    .066   gm.    of 

HPH.O,- 

Take  5  gms.  of  the  acid,  dilute  it  with  a  small  quan- 
tity of  water,  add  a  few  drops  of  phenolphthalein  T.  S., 

N 
and  titrate  with  —  KOH  V.  S.  until  a  very  faint  pink 

N 
color  appears.     If  8  cc.  of  the  —  alkali  are  used,  the 

5  gms.  contain  8  X  .066  =  .528  gm. 


5  :  .528  : :  IOO  :  x.         x  =  10.56$ 


6.6  gms.  of  the  U.  S.  P.  acid  should  require  for  neu 

N 
tralization  10  cc.  of  —  KOH  V.  S. 

Acidum  Lacticum,  HC3H5O3  =  j /979._ An  or- 
ganic acid  containing  75  per  cent.,  by  weight,  of  abso- 
lute lactic  acid  and  25  per  cent,  of  water. 

5  gms.  of  lactic  acid  are  slightly  diluted  with  water,  a 
few  drops  of  phenolphthalein  T.  S.  added,  and  then  the 

N 

KOH  V.  S.  from  a  burette,  until  a  pale-pink  color  is 

produced.     Note  the  quantity  of  normal  alkali  used, 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         8 1 

and  multiply  that  number  by  .090  gm.  to  get  the  quan- 
tity of  absolute  acid  in  the  5  gms.  taken. 

HC3H603  +  KOH  =  KC3H603  +  HQO, 

go  gms.  =     56  gms.  =      1000  cc.  —  KOH  V.  S. 

and  i  cc.  of  y  KOH  =  .090  gm.  of  HC3H5O3- 

N 
If  40  cc.  of  —  KOH  are  required  for  neutralization 

of  the  5  gms.  of  the  lactic  acid,  then 

X  40  -09  =  3-6o  gms. 
5  :  3.6  :  :  100  :  x.     x  =  72% 

Acidum  Nitricum  (Nitric  Acid),  HNO3=  j  *^2'89. 

— The  U.  S.  P.  acid  contains  68  per  cent.,  by  weight,  of 
absolute  nitric  acid  and  32  per  cent,  of  water. 

Take  3  gms.  of  nitric  acid,  dilute  with  a  little  water, 
add  a  few  drops  of  phenolphthalein  T.  S.,  and  then 

N 
pass    into   the   mixture    from  a  burette  --  potassium 

hydroxide  V.  S.  until  neutralization  is  effected,  and  the 
liquid  acquires  a  faint  pink  color. 
Apply  the  following  equation  : 

HN03  +  KOH  =  KN03  +  H2O. 

63  gms.         56  gms.  =    1000  cc.  —  KOH  V.  S. 

N 

Thus  each  cc.  of  —  KOH  V.  S.  required  before  neu- 
tralization is  effected  represents  0.063  gm.  of  absolute 
nitric  acid. 


82         A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

N 
If  30  cc.  of  the  —  alkali  are  required,  then  the  3  gms. 

contain  .063  X  30  =  1.890  gms. 

3  :  1.89  :  :  100  :  ;r.         ^  =  63$ 

3.145  gms.  of  the    U.  S.  P.  acid   require   34   cc.   of 

N 
-  KOH  V.  S.,  which  corresponds  to  68$  of  absolute 

acid. 

Acidum  Nitricum  Dilutum,  U.  S.  P.,  contains  10$  of 
absolute  nitric  acid,  and  is  estimated  in  the  same  way 
as  the  nitric  acid. 

Acidum  Phosphoricum  (Phosphoric  Acid),  H3PO4 
97.  ^ — ,phe  ^  ^  p  ac}d  contains  g^  Q£  aDSOiute 
95 
orthophosphoric  acid  and  15$  of  water. 

Take  I  gm.  of  phosphoric  acid,  dilute  it  witk  water, 
add  a  few  drops  of  phenolphthalein  T.  S.,  and  titrate 

N 
with  —  potassium  hydroxide  V.  S.  until  neutralization 

is  complete  and  the  liquid  has  acquired  a  faint  pink 
color. 

2)98  2)112 

49  gms.  56  gms.  =  1000  cc.  —  KOH  V.  S. 

N 
Thus  each  cc.  of  —  KOH  required  represents  .049  gm. 

of  absolute  orthophosphoric  acid. 

If  i  gm.  of  the  acid  requires  for  neutralization  18  cc. 

of  y  KOH  V.  S.,  it  contains 

,049  X  1 8  =  .882  gm.     or     88.2^ 


A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.         83 

0.98  gm.  of  the  U.  S.  P.  acid  should  require  17  cc. 
of  —  KOH  V.  S.,  which  means  85^  of  absolute  phos- 
phoric acid. 

In  the  estimation  of  phosphoric  acid  litmus  cannot 
be  used  as  an  indicator,  for  the  disodic  or  dipotassic 
hydric  phosphate  (Na2HPO4  or  K2HPO4)  which  is 
formed  when  the  standard  alkaline  solution  is  added  to 
free  tribasic  phosphoric  acid  is  slightly  alkaline  to  lit- 
mus, but  not  to  phenolphthalein. 

It  is  recommended,  therefore,  in  order  to  estimate 
phosphoric  acid  alkalimetrically,  to  prevent  the  forma- 
tion of  soluble  phosphate  of  the  alkali,  and  to  bring 
the  acid  into  a  definite  compound  with  an  alkaline 
earth  as  follows : 

The  free  acid  in  a  diluted  state  is  placed  in  a  flask 
and  a  known  volume  of  normal  alkali  in  excess  added 
in  order  to  convert  the  whole  of  the  acid  into  a  basic 
salt.  A  few  drops  of  rosolic  acid  are  now  added,  and 
sufficient  neutral  BaCl2  solution  poured  in  to  combine 
with  the  phosphoric  acid.  The  mixture  is  heated  to 
boiling,  and  while  hot  the  excess  of  alkali  is  titrated 

with  _  acid, 
i 

The  suspended  basic  phosphate,  together  with  the 
liquid,  possesses  a  rose-red  color  until  the  last  drop  or 
two  of  acid,  after  continuous  heating  and  agitation, 
gives  a  permanent  white  or  slightly  yellowish  milky 
appearance,  when  the  process  is  ended. 

The  volume  of  normal  alkali,  less  the  volume  of  nor- 
mal acid,  represents  the  amount  of  alkali  required  to 
convert  the  phosphoric  acid  into  a  normal  trisodic  or 
tripotassic  phosphate. 


84        A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

H3P04  +  3KOH  =  K3P04  +  3H20. 

3)98  3)168  N 

32.66  gms.      56  gms.  =  1000  cc.  of  —  KOH  V.  S. 

N 
Thus  i  cc.  of  —  alkali  =  .03266  gm.  of  H3PO4. 

Diluted  phosphoric  acid  is  estimated  in  the  same 
manner. 

Phosphoric  Acid  may  also  be  estimated  by  Stolba's 
method,  as  Ammonio-magnesian  Phosphate. 

O.2  gm.  of  phosphoric  acid  is  supersaturated  with 
ammonia  water,  so  as  to  convert  all  of  the  acid  into 
ammonium  phosphate  and  leave  an  excess  of  the 
alkali. 

H3PO4  +  2NH4OH  =  (NH4)2  HPO4  +  2HaO. 
98  132 

An  excess  of  magnesia  mixture*  is  now  added  in 
order  to  precipitate  all  of  the  phosphoric  acid  in  the 
form  of  ammonio-magnesian  phosphate. 

(NH4),HP04  +  MgS04  =  Mg(NH4)P04  +  NH4HSO4 
132  137 

The  precipitate  is  washed,  first  with  ammonia  water, 
and  then  the  ammonia  is  entirely  removed  by  washing 
with  alcohol  of  50$  or  60$  strength. 

The  precipitate   is  now  dissolved  in  a  measured  ex- 

N 
cess  of  —   hydrochloric    acid    V.    S.,    a    few   drops    of 

methyl-orange  T.  S.  added,  and   the   excess   of  acid 

*  Magnesia  Mixture.— Dissolve  TO  gms.  of  magnesium  sulphate 
and  20  gms.  of  ammonium  chloride  in  80  cc.  of  water,  add  42  cc.  of 
ammonia  water,  set  aside  for  a  few  days  in  a  well-stoppered 
and  filter.  It  should  never  be  used  freshly  made. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.        85 

N 
found  by  titrating  back  with  —   potassium    hydrate. 

N 
The  difference  between   the  number  of  cc.  of  —  HC1 

N 

added  and  the  quantity  of  —  KOH  used  gives  the  quan- 
tity of  HC1  which  went  into  combination  with  the  am- 
monia-magnesian  phosphate. 


Mg(NH4)P04  +  2HC1  =  NH4HaP04  +  MgCla. 

137  72.8 

By  consulting  the  equations  given,  it  will  be  seen 
that  72.8  gms.  of  HC1  are  equivalent  to  137  gms.  of 
Mg(NH4)PO4,  or  132  gms.  of  (NH4)2HPO4,  or  98  gms. 
of  H3PO4. 

This  means  that   1000  cc.  of  a  decinormal   [  —  ]  solu- 


tion  of   HC1,  containing   3.64  gms.  of  the   acid,  repre- 
sents ^   of  each  of  these  quantities  ;  and   one  cc.  of 

N 
-  HC1  thus  represents  0.0049  §m-  of  phosphoric  acid. 

In  this  estimation  care  must  be  taken  that  all  free 
ammonia  is  removed  from  the  precipitate,  and  that  the 
whole  of  the  ammonia-magnesian  phosphate  is  decom- 

N 

posed  by  the  acid  before  titration  with  the  —  alkali. 

10 

This  may  be  insured  by  using  a  rather  large  excess  of 
the  acid  and  warming. 

Example. — To  the  precipitate  of  ammonia-magne- 
sian phosphate  obtained  from  0.2  gm.  of  phosphoric 

N 
acid,  50  cc.  of  —  HC1  are  added.    In  titrating  back  15.3 


86        A   TEXT-BOOK   OF   VOLUMETRIC    ANALYSIS. 

N 
cc.  of   —  KOH  are  required.     Hence  34.7  cc.  of  the  acid 

went  into  combination  with  the  double  salt. 
Then  34.7  X  .0049  —  0.17003  gm., 

.17003  X  100 
and  —  —          =  85.01$  of  absolute  phosphoric 

acid.     This  method  is  said  to  give  good  results. 
Acidum  Sulphuricum,  H2SO4  =  j  97g82.—  U.  S.  P. 

sulphuric  acid  contains  92.5  per  cent.,  by  weight,  of  ab- 
soluted  sulphuric  acid  and  7.5  per  cent,  of  water. 

Aromatic  Sulphuric  Acid  U.  S.  P.  contains  18.5$  of 
absolute  sulphuric  acid,  by  weight. 

Diluted  Sulphuric  Acid  U.  S.  P.  contains  10$  by 
weight  of  absolute  sulphuric  acid.  Operate  upon  I 
gm.  of  the  strong  acid  or  upon  5  gms.  of  either  dilute 
or  aromatic  sulphuric  acid. 

One  gm.  of  sulphuric  acid  is  diluted  with  about  10  cc. 
of  water.  Add  a  few  drops  of  phenolphthalein  T.  S. 

N 
and  titrate  with  —  potassa  V.  S.  until  the  acid  is  neu- 

tralized  and   the   solution   has  acquired   a   faint    pink 

N 
color.     Each  cc.  of  —  alkali  solution   represents   0.049 

gm.  of  absolute  sulphuric  acid. 

The  reaction  is  shown  by  the  following  equation  : 

H3S04  +  2KOH  =  K2S04  +  2H,0. 

2)98  2)112  N 

49  gms.          56  gms.    =  1000  cc.  of  —  KOH  V.  S. 


N 
If  18  cc.  of  —  KOH  V.  S.  are  required  for  the  com- 

plete neutralization  of  the  sulphuric  acid,  then  it  con- 

tains 1  8  X  .049  gm.  =  0.882  gm. 

I  :  0.882  :  :  100  :  x     x  =  88.2$  absolute  sulphuric  acid. 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         87 

Diluted  Sulphuric  Acid  is  estimated  in  the  same 
way.  Operate  upon  5  gms.  instead  of  upon  I  gm. 

Aromatic  Sulphuric  Acid  contains  ethyl  sulphuric 
acid.  Therefore  in  estimating  the  sulphuric  acid  in 
this  preparation  it  must  be  boiled  with  water  for  a  few 
minutes  so  as  to  decompose  the  ethyl  sulphuric  acid. 
The  mixture  is  then  allowed  to  cool,  and  titrated  in 

N 
the  usual  manner  with  —  KOH  V.  S.,  using  phenol- 

phthalein  as  indicator. 

The  U.  S.  P.  requires  that  4.89  gms.  when  mixed  with 
15  cc.  of  water  and  boiled  for  several  minutes  should, 
after  cooling,  be  neutralized  by  not  less  than  18.5  cc.  of 

-KOH. 
i 

Acidum  Tartaricum  (Tartaric  Acid),  H2C4H4O6  = 


#  .  —  Dissolve  3.75  gms.  of  tartaric  acid  in  suffi- 

cient water  to   make  a   solution,  add   a  few  drops  of 
phenolphthalein  T.  S.,  and  then  pass  into  the  solution 

N 
from  a  burette  —  potassium  hydroxide  V.  S.  until  a 

faint  pink  tint  is  acquired  by  the  solution,  and  apply 
the  equation 


H,C4H406  J_  2KOH  =  K,C4H4O6  +  2H2O, 

2)150  2)112  N 

75  gms.  56  gms.  =  1000  cc.  —  KOH  V.  S. 


Thus  each  cc.  required  for  the  neutralization  of  the 
acid  represents  0.075  gm.  If  50  cc.  are  required,  then 
50  X  .075  —  3.75  gms,  or 


88 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


TABLE  SHOWING  THE  APPROXIMATE  NORMAL   FACTORS,  ETC.,   FOR 
THE  ACIDS. 


Acid. 

Formula. 

Molecular 
Weight. 

Normal 
Factors.* 

Acetic  ... 

HC2H3O2 

60 

060 

Citric.  

H3C6H507.H20 
HBr 

210 

81 

.070 

08  1 

Hydrochloric       

HC1 

q5  A 

o^6j. 

Hypophosphorous  

HPH2O2 

66 

066 

Lactic  

HC3H5O3 

QO 

OQO 

Nitric  

HNO3 

6-? 

061 

H3PO4 

08 

O4.Q 

H2SO4 

08 

.OJ.Q 

Tartaric.    .  • 

H2C4H4O6 

I  ^O 

O7C 

Phosphoric,  after  conversion  into  a  neutral  phosphate  and 

retitrating  with  —  acid  = 03266 

Phosphoric  acid,  as  ammonia-magnesian    phosphate  with 

decinormal  acid  = 0049 

*  This  is  the  coefficient  by  which  the  number  of  cc.  of  normal  solu- 
tion used  is  to  be  multiplied  in  order  to  obtain  the  quantity  of  pure 
acid  in  the  sample  analyzed. 

ESTIMATION  OF  THE  SALTS  OF  THE  ALKALINE  EARTHS. 

Standard  solution  of  hydrochloric  or  of  nitric  acid  is 
preferred  by  many  operators  for  the  titration  of  caustic 
or  carbonated  alkaline  earths. 

These  acids  have  the  advantage  over  most  other 
acids  in  forming  soluble  salts. 

The  hydroxides  may  be  estimated  by  any  of  the 
indicators,  but  as  they  readily  absorb  CO2  out  of  the 
air,  they  are  generally  contaminated  with  more  or  less 
carbonate,  and  the  residual  method  should  be  used,  i.e., 
a  known  excess  of  standard  acid  should  be  added,  the 
mixture  boiled  to  expel  any  trace  of  CO2,  and  reti- 
trated  with  standard  alkali. 

The  carbonates  are  of  course  estimated  in  the  same 
way. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.          89 

If  methyl-orange  is  used,  heat  need  not  be  employed, 
unless  it  is  impossible  to  dissolve  the  substance  in  the 
cold.  A  good  excess  of  acid  is,  however,  generally 
sufficient. 

Soluble  salts  of  calcium,  barium,  and  strontium, 
such  as  chlorides,  nitrates,  etc.,  may  be  readily  estimated 
as  follows  : 

A  weighed  quantity  of  the  salt  is  dissolved  in  water, 
cautiously  neutralized  if  it  is  acid  or  alkaline,  phenol- 
phthalein  is  added,  the  mixture  heated  to  boiling,  and 
standard  solution  of  sodium  carbonate  delivered  in 
from  time  to  time,  with  boiling  until  the  red  color  is 
permanent. 

This  process  depends  upon  the  fact  that  sodium 
carbonate  forms  with  soluble  salts  of  these  bases  in- 
soluble and  neutral  carbonates. 

CaCl,  +  Na,CO3  =  CaCO3  +  2NaCl. 
Ba(N03)2  +  Na2C03  =  BaCO3  +  2NaNO3. 

Magnesium  salts  cannot  be  estimated  in  this  way,  as 
magnesium  carbonate  affects  the  indicator. 

The  alkaline  earth  salts  may  also  be  estimated  by 
dissolving  them  in  water,  precipitating  the  base  as  car- 
bonate, with  an  excess  of  ammonium  carbonate  and 
some  free  ammonia. 

The  mixture  is  heated  for  a  few  minutes,  and  the 
carbonate  separated  by  filtration,  thoroughly  washed 
with  hot  water  till  all  soluble  matters  are  removed,  and 
then  titrated  with  normal  acid  V.  S.  as  carbonate. 

Normal    Sodium     Carbonate    V.   S.— Na2CO3  = 

]  *  06       contains  #5*          [  gms.  in  I  litre. — This  solu- 
tion is  made  by  dissolving  53  gms.  of  pure  sodium  car- 


90         A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

bonate  (anhydrous)  previously  ignited  and  cooled,  in 
distilled  water,  and  diluting  to  I  litre  at  15°  C.  (59°  F.). 

If  pure  salt  is  not  at  hand  the  solution  may  be 
made  as  follows : 

About  85  gms.  of  pure  sodium  bicarbonate,  free  from 
thiosulphate,  chloride,  etc.,  are  heated  to  dull  redness 
(not  to  fusion)  for  about  fifteen  minutes  to  expel  one 
half  of  the  CO2 ;  it  is  then  cooled  under  a  desiccator. 
When  cool,  weigh  off  53  gms.  and  dissolve  it  in  distilled 
water  to  I  litre  at  15°  C.  (59°  F.).  This  solution  should 

N 
neutralize  —  acid  V.  S.  volume  for  volume. 

i 

Liquor  Calcis  (Lime-water),  Ca(OH)a  =  j  ^3'83.- 

The  U.  S.  P.  directs  lime-water  to  be  estimated  with 
deanormal  oxalic  acid  V.  S.,  using  phenolphthalein  as 
indicator. 

Take  50  cc.  of  lime-water,  add  a  few  drops  of  phenol- 

N 
phthalein,  and  then  carefully  from  a  burette  —  oxalic 

acid  V.  S.  until  the  red  color  is  just  discharged.     20  cc. 

N 

of  the  —  acid  V.  S.  should  be  required  for  the  neutra- 
10 

lization.  This  corresponds  to  0.14  (0.148)  per  cent,  of 
calcium  hydroxide. 


Ca(OH),  +  H2C204 .  2H20  =  CaC2O4  +  4H,O. 
20)74  20)126 

3.7  gms.  6  3  gms.  or  1000  cc.  —  V.  S. 

10 

N 
Each  cc.  of  —  oxalic  acid  V.  S.  represents  .0037  gm. 

of  Ca(OH)2. 


U  i  *  B  • 

A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.         91 


Then  .0037  X  20  —  0.074  gm. 

.074  X  100 

— =  0.148$ 

Syrupus  Calcis,  U.  S.  P.  (Liquor  Calcis  Saccharatus, 
Br.  P.). — This  is  estimated  in  exactly  the  same  way  as 
the  lime-water,  except  that  the  solution  is  weighed  for 
analysis,  not  measured,  as  its  specific  gravity  is  much 
higher  than  that  of  water. 

Operate  upon  about  25  grammes. 


Calcium  Carbonate,  CaCO3=     ^'.—  No  meth- 


od is  given  for  the  estimation  of  calcium  carbonate  in 
the  Pharmacopoeia,  but  the  following  process  may  be 
used  : 

One  gm.  of  calcium  carbonate  is  mixed  with  5  cc.  of 
water.  A  measured  excess  of  normal  sulphuric  acid 
V.  S.  is  now  added,  and  the  solution  boiled  to  drive  off 
the  CO2.  Then  add  a  few  drops  of  phenolphthalein 

N 
T.  S.,  and  titrate  with  -  alkali  V.  S.  until  a  faint  pink 

color  is  obtained. 

N 
Note  the  quantity  of  —  alkali  used,  and  deduct  this 

N 
from  the  quantity  of  —  acid  first  added,  and  the  remain- 

der will  represent  the  amount  of  acid  which  combined 
with  the  calcium. 

N 
Each    cc.  of    —  acid    V.  S.    represents  .05    gm.   of 

CaC03. 

CaC03  4-  H,S04  =  CaSO,  +  H2O  +  COa. 

2)100  2)98  N 

50  gms-  49  gms.  or  1000  cc.  —  acid  V.  S. 


92         A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

N 
Assuming  that  30  cc.  of  —  H2SO4  V.  S.  were  added  to 

N 
the  i  gm.  of  CaCO3,  and  that  11  cc.  of  —  KOH  V.  S. 

were  required  to  bring  the  mixture  back  to  neutrality, 

N 
then    19  cc.   of   —   H2SO4   were   actually  required   to 

saturate  the  CaCO3. 

Therefore  .05  X  19  =  -95  gm.,  or  95$. 

Calcium    Bromide,    CaBr2  =  j  *^g43 .—This   salt 

when  dissolved  in  water  may  be  estimated  directly  with 
normal  solution  of  sodium  carbonate. 

One  gm.  of  the  salt  is  dissolved  in  a  small  quantity  of 
water.  The  solution  is  neutralized,  if  it  is  acid  or 
alkaline,  heated  to  boiling,  a  few  drops  of  phenol- 

N 
phthalein  T.  S.  added,  and  the  solution  titrated  with  - 

sodium  carbonate  V.  S.  delivered  cautiously,  with  boil- 
ing, until  the  red  color  is  permanent. 

CaBr2  +  Na2CO3  =  CaCO3  +  2NaBr. 
2)200  2)106 

TOO  gms.          53  gms.  or  1000  cc.  —  Na2CO3  V.  S. 

N 

Each  cc.  of  —  Na2CO3  V.  S.  represents  o.i  gm.  of  cal- 
cium bromide. 

If  9  cc.  are  used,  the  salt  contains  o.i  X  9  —  .9  gm., 
or  90$,  of  pure  CaBr2. 

Another  way  is  to  add  an  excess  of  ammonium-car- 
bonate solution  with  some  free  ammonia  to  the  solu- 
tion of  calcium  bromide,  in  order  to  precipitate  all  the 
base  in  the  form  of  carbonate.  The  carbonate  is  then 


A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.         93 

separated  by  filtration,  thoroughly  washed  with  hot 
water  to  remove  all  soluble  matters,  and  then  titrated 
as  directed  for  carbonate. 

CaBr,  =  CaCO,  =  H2SO4. 

2)200       2)100         2)98 

100  gms.    50  gms.    49  gms.  or  1000  cc.  —  V.  S. 

N 
Each  cc.  of  —acid  thus  represents  o.i   gm.  of  CaBr2. 

See  U.  S.  P.  method,  page  103. 

Calcium   Chloride,    CaCl2  = -L110^5.  — This   salt 

(      I  IO.o 

may  be  estimated  in  exactly  the  same  way  as  described 
for  the  bromide. 

CaCl2  +  Na2C03  =  CaCO3  +  2NaCl. 
2)110.8          2)106 

55.4  gms.         53  gms.  or  1000  cc.  —  V.  S. 

N 
i  cc.  —  Na2CO3  —  .0554  gm.  of  CaCl,. 

CaCl,  =  CaCO3  =  H2SO4 . 
2)110.8         2)100  2)98 

55-4  50  49  gms.  or  1000  cc.  —  V.  S. 

i 

N 
i  cc.  -  H2SO4  =  .0554  gm.  of  CaCl3. 

Barium  Chloride,  BaCl2,  and  Barium  Nitrate, 
Ba(NO3)a. — These  two  salts  are  estimated  in  the  same 
way  as  the  soluble  salts  of  calcium  noted  in  the 
previous  chapter. 

The  factor  for  BaCl2  is         0.10385  gm., 
the  factor  for  Ba(NO3)2  is  0.13045  gm., 
using  normal  volumetric  solutions. 


94         A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

Strontium  Lactate,Sr(C,H.O1),+3H,O=  j  .^jjj5. 

— 1-33  gms-  °f  the  salt,  rendered  anhydrous  before 
being  weighed,  by  careful  drying  at  110°  C.  (230°  F.), 
is  ignited,  until  most  of  the  carbon  has  disappeared, 
and  then  mixed  with  10  cc.  of  water.  A  few  drops  of 
methyl  orange  T.  S.  are  now  added,  and  the  mixture 

N 
titrated  with  --   H2SO4  V.  S.  until  a  faint  red  color  is 

produced. 

N 

9.9  cc.  of  the  —  acid  should  be  required,  correspond- 
ing to  98.6$  of  the  pure  salt. 

The  first  step  in  this  process  is  to  drive  off  the  water 
of  crystallization. 

(Sr(C,H  A),  +  3H,0)  +  heat  =  Sr(C3HsOs),  +  3H,O  ; 

318.78  264.88 

then 

Sr(C,HB03),  +  60,  =  SrC03  +  5CO2  +  5H,O. 

264.88  147.15 

Thus 

Sr(C1HiOi).=  SrCOi=H1S04. 

2)264.88          2)147.15         2)98  N 

132.44  73.57  49  Sms-  or  IO°°  cc-  ~  acid  V.  S. 

N 
Thus  each  cc.  of  —  H2SO4  represents  0.13244  gm.  of 

pure  anhydrous  strontium  lactate. 
If  9.9  cc.  are  required,  then 

0.13244  X  9-9  =  I.3UI56  gms. 

'•3IIIS6XIOQ  =       ^ 
1-33 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.         95 

In  this  process,  if  the  ignition  is  carried  too  far, 
the  strontium  carbonate  is  decomposed  into  strontium 
oxide. 

Magnesium  salts  may  be  estimated  by  precipitating 
as  ammonia-magnesian  phosphate,  and  titrating  this 
precipitate  as  directed  for  phosphoric  acid. 


06         A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


CHAPTER   X. 
ANALYSIS   BY   PRECIPITATION. 

THE  general  principle  of  this  method  is  that  the 
determination  of  the  quantity  of  a  given  substance  is 
effected  by  the  formation  of  a  precipitate,  upon  the 
addition  of  the  standard  solution  to  the  substance 
under  examination.  \+* 

The  end  of  the  reaction  is  determined  in  three 
ways  : 

1.  By  adding  the  standard  solution  until  no  further 
precipitate   occurs,  as  in  the   estimation  of  chlorides, 
etc.,  by  silver  nitrate. 

2.  By  the  use  of  an  indicator.     This  may  either  be 
contained  in  the  liquid  under  analysis ;  or  used  exter- 
nally, by  frequently  bringing  a  portion  of  it  in  contact 
with  a  drop  of  the  liquid  during  the  titration. 

The  titration  is  continued  until  the  slightest  excess 
of  the  standard  solution  is  shown  by  the  production  of 
a  characteristic  reaction  with  the  indicator. 

3.  By  adding  the  standard  solution  until  a  precipi- 
tate is  produced,  as  in  the  estimation  of  cyanogen  by 
standard  silver  solution. 

The  first  of  these  endings  can  only  be  applied  with 
accuracy  to  silver  and  chlorine  estimations,  as  the 
silver  chloride  which  is  formed  is  almost  perfectly 
insoluble  and  has  a  tendency  to  curdle  closely  by 
shaking,  so  as  to  leave  a  clear  supernatant  liquid. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.         97 

Most  of  the  other  precipitates,  such  as  barium  sul- 
phate, calcium  oxalate,  etc.,  although  heavy  and  insol- 
uble, do  not  readily  and  perfectly  subside,  because 
of  their  finely  divided  or  powdery  nature.  They  must 
therefore  be  excluded  from  this  class. 

In  these  cases,  therefore,  it  is  necessary  to  find  an 
indicator  which  brings  them  into  class  2. 

The  third  class  comprises  only  two  processes,  viz., 
the  determination  of  cyanogen  by  silver,  and  that  of 
chlorine  by  mercuric  nitrate. 

ESTIMATION   OF  HALOID   SALTS. 

The  estimation  of  these  salts  is  based  upon  the 
powerful  affinity  existing  between  the  halogens  and 
silver,  and  the  ready  precipitation  of  the  resulting 
chloride,  bromide,  or  iodide. 

Standard  solution  of  silver  nitrate  is  used  for  this 
purpose,  and  for  the  sake  of  exactness  and  conven- 
ience is  made  of  decinormal  strength,  and  in  many 
cases  it  is  advisable  to  use  centinormal  solutions. 

/N\ 
The  Decinormal    —    Silver  Nitrate  V.  S.  is  offi- 

\io/ 

cial.     AgN03  =  -j     *^55     I^'955  igms.  are  contained 
1*169.7       16.97    f* 

in  i  litre. — Dissolve  16.97  gms.  of  pure  silver  nitrate 
in  sufficient  water  to  make,  at  or  near  15°  C.  (59°  F.), 
exactly  1000  cc.  I  litre  of  this  solution  thus  contains 
TV  of  the  molecular  weight  in  grammes  of  silver 
nitrate.  It  is  therefore  a  decinormal  solution. 

If  pure  crystals  of  silver  nitrate  are  not  readily  ob- 
tainable, and  pure  sodium  chloride  is  at  hand,  a  solu- 
tion of  the  silver  nitrate  may  be  made  of  approximate 


98         A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

strength,  a  little  stronger  than  necessary,  and  then 
standardized  by  means  of  the  sodium  chloride,  as  fol- 
lows :  0.117  gm.  of  sodium  chloride  is  dissolved  in 
water,  and  a  burette  is  filled  with  the  solution  of  silver 
nitrate  to  be  standardized.  The  silver  solution  is  now 
slowly  added  from  the  burette  to  the  sodium-chloride 
solution  contained  in  a  beaker  until  no  more  precipi- 
tate of  silver  chloride  is  produced. 

If  neutral  potassium  chromate  is  used  as  an  indi- 
cator, the  end  of  the  reaction  is  shown  by  the  appear- 
ance of  yellowish-red  silver  chromate.  This  indication 
is  extremely  delicate.  The  silver  nitrate  does  not  act 
upon  the  chromate  until  all  of  the  chloride  is  converted 
into  silver  chloride. 

In  the  above  reaction  20  cc.  of  silver  nitrate  should 
be  required.  But  since  the  silver-nitrate  solution  is 
too  strong,  less  of  it  will  complete  the  reaction,  and 
the  solution  must  be  diluted  so  that  exactly  20  cc.  will 
be  required  to  precipitate  the  chlorine  in  0.117  gm-  °f 
NaCl. 

Thus  if  17  cc.  are  used,  each  17  cc.  must  be  diluted 
to  20  cc.,  or  each  170  cc.  to  200  cc.,  or  the  entire  re- 
maining solution  in  the  same  proportion. 

After  dilution  a  fresh  trial  should  always  be  made. 

Nitrate  of  silver  solution  should  be  kept  in  dark 
amber-colored,  glass-stoppered  bottles,  carefully  pro- 
tected from  dust. 

Titration  by  decinormal  silver  nitrate  V.  S.  may  be 
managed  in  various  ways,  adapted  to  the  special  prep- 
aration to  be  tested. 

I.  In  most  cases  it  is  directed  by  the  U.  S.  P.  to  be 
used  in  the  presence  of  a  small  quantity  of  potassium 
chromate  T.  S. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.         99 

2.  In  some  cases  it  is  added  until  the  first  appear- 
ance of  a  permanent  precipitate,  as  in  potassium  cya- 
nide and  hydrocyanic  acid. 

3.  It  may  be  used  in  all  cases  without  an  indicator 
by  observing  the  exact  point  when  no  further  precipi- 
tate occurs.     But  since  this  consumes  too  much  time 
in  waiting  for  the  precipitate  to  subside,  so  as  to  render 
the   supernatant  liquid   sufficiently  clear  to   recognize 
whether  a  further  precipitate  is  produced  by  the  addi- 
tion of  the  silver  solution,  it  is  impracticable.     It  may, 
however,  be   practised   in  the   case   of  ferrous   iodide, 
where  the  addition  of  potassium  chromate  T.  S.  would 
be  improper,  since  it  reacts  with  the  iron. 

4.  It  may  be  added  in  definite  amount,  known  to 
be  in  excess-  of  the  quantity  required,  and  the  excess 
measured  back  by  titration  with  decinormal  potassium 
sulphocyanate  V.  S.,  or  even  with  decinormal  sodium 
chloride  V.  S.  (residual  titration). 

N 

In  case  an  excess  of  the  -  -  silver  nitrate  V.  S.  is 

10 

added  accidentally,  it  is  only  necessary  to  add  a  defi- 

N 

nite  volume  of  a  —  solution  of  the  salt  under  exami- 
10 

N 
nation,  and  finish  the  titration  with  -  -  silver  nitrate, 

deducting,  of  course,  the  same  number  of  cc.  of  silver 
solution  as  has  been  added  of  the  salt  solution. 

Ammonium   Bromide,   NH4Br  =  -j  #97-77. — 3 

of  the  salt  are  dried  at  100°  C.  (212°  F.)  and  dissolved 
in  water  to  the  measure  of  100  cc.  10  cc.  of  this  solu- 
tion are  placed  in  a  beaker,  a  few  drops  of  potassium 
chromate  T.  S.  added,  and  then  the  decinormal  silver 


100      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

nitrate  V.  S.  carefully  added  from  a  burette,  until  a 
permanent  red  coloration  is  produced.  The  red  col- 
oration is  due  to  the  formation  of  red  chromate  of 
silver,  which  takes  place  after  all  of  the  bromine  has 
combined  with  the  silver.  Apply  the  equation  : 

NH4Br  +  AgNO3  =  AgBr  +  NH4NO,. 
10)97.77  10)169.7  N 

9-777  gms.         16.97  gms.  or  1000  cc.   —  AgNO3  V.  S. 


N 
Thus  each  cc.  of  the  —  V.  S.  represents  .009777  gm. 

of  NH4Br. 

3  gms.   of  the  U.  S.  P.  salt  should  require  30.9  cc. 

of  5  AgNO,  V.  S. 

But  as  a  rule  this  salt  contains  an  impurity  (am- 
monium chloride)  which  will  be  precipitated  by  the 
silver  nitrate  as  well  as  the  bromide.  The  presence  of 
this  impurity  must  therefore  be  taken  into  account  in 
calculating  the  percentage  of  bromide. 

NH4C1  +  AgNO,  ==  AgCl3  +  NH4NO3. 

io)53.38 


_ 
5.338  16.97  gms.  =  1000  cc.  of  —  V.  S. 

The    amount    of  the   salt   examined    equivalent  .to 

N 
IOOO  cc.  of   —    silver  solution   is    first   calculated    by 

simple  proportion  : 

30.9  cc.  :  .3  gm.  :  :  1000  cc.  :  x.         x  =  9.708. 

Then 

9777  -9708  =y.       y 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       IO1 

N 
.069  =  the  excess  of  —  AgNO3  V.  S.  used  up  by 

the  ammonium  chloride,  reckoned  in  terms  of  bromide 
(NH4Br) ;  and  since  5.338  gms.  of  NH4C1  =  9777  gms. 
of  NH4Br,  the  excess  which  NH4C1  can  consume  is 
represented  by  9.777  —  5.338  =  4-439-  Therefore,  as 

4-439  :  5-338  : :  .069  :  z.         z  =  0.08297. 

0.08297  =  the  amount  of  ammonium  chloride  present 
in  x  grammes  of  the  sample  taken. 

Lastly,  calculate  the  percentage  by  simple  propor- 
tion : 

9.708  :  .0829  : :  100  :  P.     P=  0.85$  of  NH4C1. 

Lithium   Bromide,  LiBr  =  |  J?6'77.— Dissolve  0.3 

(    °7 

gm.  of  dry  lithium  bromide  in  10  cc.  of  water,  add  2 
drops  of  potassium  chromate  T.  S.,  and  then  titrate 
with  decinormal  silver  nitrate  V.  S.  until  a  permanent 
red  color  of  silver  chromate  makes  its  appearance. 

N 
0.3  gm.  of  the  U.S.  P.  salt  requires  35.3  cc.  of  --  V.  S. 

LiBr    +  AgNO3  =  AgBr  +  LiNO3. 

10)86.77  10)169  -7  N 

8.677  gms.         16.97  gms.  or  1000  cc.  —  AgNO3  V.  S. 

Thus  each  cc.  of  —  AgNO3  V.  S.  =  0.008677  gm.  cf 
pure  lithium  bromide. 

Potassium  Bromide,  KBr  =  j  *j*8'79.— Operate 
upon  o.i  gm.  of  the  salt  dissolved  in  about  10  cc.  of 


IO2       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

water.     Add  a  few  drops  of  potassium  chromate  T.  S., 

N 
and  titrate  with  —  AgNO3  V.  S.  until  a  permanent  red 

color  of  silver  chromate  is  produced.  According  to  the 
U.  S.  P.,  0.5  gm.  of  the  well-dried  salt  should  require 

42.85  cc.  of  ^  AgN03  V.  S. 

KBr  +  AgNO3  =  AgBr+  KNO3. 
io)"8-79       10)169.7  N 

11.879  Sms-     l6-97  gms.  or  1000  cc.  —  AgNO3  V.  S. 

Thus  each  cc.  represents  .011879  gm.  of  KBr.  Po- 
tassium chloride  is  a  common  impurity;  to  calculate  it» 
proceed  as  for  NH4C1,  74.4  of  KC1  being  equal  to 
118.79  of  KBr- 

Sodium  Bromide,  NaBr  =  j  *j°2'76-—  This  salt  is 

tested  in  exactly  the  same  manner  as  the  potassium 
bromide.  A  convenient  quantity  to  operate  upon  is 
O.I  gm. 

The  U.  S.  P.  directs  that  0.3  gm.  of  the  well-dried 
salt  be  dissolved  in  10  cc.  of  water,  two  drops  of  potas- 
sium chromate  T.  S.  added,  and  the  mixture  titrated 
with  decinormal  silver  nitrate  V.  S.  until  a  permanent 
red  color  of  silver  chromate  appears. 

Note  the  number  of  cc.  required  to  produce  this 
effect,  and  multiply  this  number  by  the  factor  0.010276 
gm.  This  will  give  the  quantity  of  NaBr  present  in 
the  sample  taken. 

According  to  the  U.  S.  P.,  not  more  than  29.8  cc.  of 
the  standard  silver  solution,  corresponding  to  at  least 
97.29$  of  the  pure  salt,  should  be  required. 

The  chloride  which  is  present  as  an  impurity  may 


A   TEXTBOOK   OF   VOLUMETRIC   ANALYSIS.       1  03 

be  calculated  in  the  same  manner  as  ammonium  chlo- 
ride, 5.837  gms.  of  the  chloride  being  equal  to  10.276 
gms.  of  sodium  bromide. 

Calcium   Bromide,   CaBr2  j  **99'43.—  This  salt  may 

be  tested  as  described  on  page  92. 

The  U.  S.  P.  method  is  as  follows:  0.25  gm.  of  the 
well-dried  salt  is  dissolved  in  10  cc.  of  water;  2  drops 
of  potassium  chromate  T.  S.  are  then  added,  and  the 
solution  titrated  with  decinormal  silver  nitrate  V.  S. 
until  a  permanent  red  color  is  produced.  25  cc.  of  the 
standard  silver-nitrate  solution  should  be  required  to 
produce  this  result,  corresponding  to  99.7$  of  the  pure 
salt,  a  greater  amount  of  the  standard  solution  indicat- 
ing the  presence  of  calcium  chloride,  a  smaller  amount 
indicating  other  impurities. 

CaBr2  +  2AgNO3  =  2AgBr  +  Ca(NO3)2. 

2)199.43         2)339.4 

10)99.715      10)169.7  N 

9.9715  gms.  16.97  gms.  or  1000  cc.  —  AgNO3  V.  S- 

N 
Thus  each  cc.  of  —  AgNO3  V.  S.  represents  .0099715 

gm.  of  CaBr2. 

Therefore  25  cc.  represent  .0099715  X  25  =  0.2492875 
gm. 

.2492875  X  IPO 


0.25 


^         , 


Strontium   Bromide,  SrBr,  +  6H2O  =  j 

This  salt   is   tested   volumetrically,  according   to   the 
U.  S.  P.,  in  the  following  manner: 

0.3  gm.  of  strontium  bromide,  rendered  anhydrous  by 


104      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

thorough  drying  before  being  weighed,  is  dissolved  in 
10  cc.  of  water,  3  drops  of  potassium  dkchromate  T.  S. 
are  added,  and  then  the  decinormal  silver  nitrate  V.  S. 
is  poured  in  from  a  burette  until  all  of  the  bromide  has 
combined  with  the  silver  nitrate  and  a  permanent  red 
coloration  is  produced. 

Not  more  than  24.6  cc.  of  decinormal  silver  nitrate 
V.  S.  should  be  required,  corresponding  to  at  least  98$ 
of  the  pure  salt. 

SrBr2  +  2AgN03  =  2AgBr  +  Sr(NO3)2. 

2)246.82         2)339.4 
10)123.41        10)169.7  N 

12.341  gms.     16.97  gms.  or  1000  cc.  —  AgNO3  V.  S. 

N 
Thus  each  cc.  of  —  AgNO3V.  S.  represents  0.012341 

gm.  of  strontium  bromide. 

Zinc  Bromide,  ZnBr2  =  |  ^'62.— This  salt  is  es- 
timated as  follows :  0.3  gm.  of  the  dry  salt  is  dissolved 
in  10  cc.  of  water,  2  drops  of  potassium  chromate  T.  S. 
are  added,  and  then  decinormal  silver  nitrate  V.  S.  is 
poured  in  from  a  burette  until  all  of  the  bromide  has 
combined  with  silver  nitrate,  and  a  permanent  red 
color  is  produced.  Note  the  number  of  cc.  of  the 
standard  silver  solution  used,  and  multiply  this  num- 
ber by  the  factor  shown  by  the  following  equation,  to 
obtain  the  amount  of  pure  zinc  bromide  in  the  quan- 
tity taken : 

ZnBr2  +  2AgNO3  =  2AgBr  +  Zn(NO3)2. 
20)224.62        20)339.4  N 

11.231  gms.     16.97  gms.  or  1000  cc.  —  AgNO3  V.  S. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       IO5 

Thus  each  cc.  represents  .011231  gm.  of  pure  ZnBr3. 
The  U.  S.  P.  salt  should  require  26.7  cc.  of  decinormal 
silver  nitrate  V.  S.  to  produce  the  desired  reaction,  cor- 
responding to  not  less  than  99.95$  of  the  pure  salt. 

Thus  0.011231  X  26.7  =  0.2998677  gm. 

0.2998677  X  IPO 

Potassium    Iodide    KI  =  .—  This  is   esti- 


ide, KI  =  j 


mated,  according  to  the  U.  S.  P.,  in  a  manner  similar  to 
the  haloid  salts  just  considered. 

0.5  gm.  of  the  well-dried  salt  is  dissolved   in  10  cc. 
of  water,  2  drops  of  neutral  potassium  chromate  T.  S. 

N 
are  added,  and  then  the  —  AgNO3  V.  S.  slowly  added 

from  a  burette  until  a  permanent  red  color  of  silver 
chromate  is  produced.  Not  more  than  30.25  cc.  nor 
less  than  30  cc.  of  decinormal  silver  nitrate  V.  S.  should 
be  required.  This  quantity  corresponds  to  99.5$  of  the 
pure  salt. 

KI    +  AgNO3 

10)165.56       10)169.7 


N 


16.556  gms.     16.97  gms.  or  1000  cc.  —  AgNO3  V.  S. 

N 
Each  cc.  of  -  -  AgNO3  V.  S.  thus  corresponds  to 

0.016556  gm.  of  potassium  iodide. 

Thus  0.016556  X  30  =  0.49668  gm. 

0.49668  X  IQQ  =  99  3^ 


106      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

Potassium    iodide   may  also  be  estimated  volumet- 

N 
rically  by  —  mercuric  chloride  V.  S.,  the  termination 

of  the  operation  being  indicated  by  the  formation'of  a 
red  precipitate. 

4KI  +  HgCla  =  2KC1  +  HgI2.2KI  (soluble),     (i) 

2HgI2.       .     (2) 


This  process  originated  with  M.  Personne,  and  is 
founded  on  the  fact  that  if  a  solution  of  mercuric  chlo- 
ride be  added  to  one  of  potassium  iodide,  in  the  pro- 
portion of  one  equivalent  of  mercuric  chloride  to  four 
of  potassium  iodide,  red  mercuric  iodide  is  formed, 
which  dissolves  at  once  to  a  colorless  solution.  The 
slightest  excess  of  mercuric  chloride  will  cause  a  bril- 
liant red  precipitate  to  make  its  appearance,  HgI2. 

4KI    +    HgCl2  =  2KCl+HgI3.2KI  (soluble). 
20)662.24       20)270.54 

33.112  gms.     13.527  gms.  or  1000  cc.  of  standard  solution. 

Thus  each  cc.  of  standard  solution  of  the  above 
strength  represents  0.033112  gm.  of  potassium  iodide, 
which  means  that  I  cc.  is  the  largest  quantity  of  this 
standard  solution  which  can  be  added  to  0.033112  gm. 
of  potassium  iodide  without  producing  a  permanent 
precipitate. 

The   above   solution   of    mercuric   chloride    is   not 

N 

strictly  a  —  V.  S.    Potassium  iodide  is  a  univalent  salt  ; 
20 

and  since  four  molecules  of  it  are  precipitated  by  one 
molecule  of  mercuric  chloride,  the  latter  is  chemically 
equivalent  to  four  atoms  of  hydrogen  ;  and  \  of  its 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       IO? 

molecular  weight  in  grammes,  dissolved    in  water  to 

N 
one  litre,  is  a  normal  solution,  and  ^  of  this  is  a  — 

V.  S. 

The  author  of  this  process  states  that  neither  chlo- 
rides, bromides,  nor  carbonates  interfere  with  the  re- 
action. 

Sodium    Iodide,    Nal   =   j  *j49'  JJ3.—  Dissolve    0.5 

gm.   of   the  well-dried  salt  in  10  cc.   of  water,  add  2 
drops   of   potassium    chromate    T.  S.,  and  then    pass 

N 
into  the  solution  from  a  burette  —  AgNO3  V.  S.  until 

a  permanent  red  coloration  is  produced. 

Note  the  number  of  cc.  used,  and  multiply  this  by 
the  factor. 

Nal    +   AgNO3  =  Agl  +  NaNO3  . 
10)149.53         10)169.7  N 

I4-953  Sms-      J6'97  gms-  °r  1000  cc.   —  AgNO3  V.  S. 

N 
Each  cc.  of  —  AgNO3  V.  S.  represents  0.014953  gm. 

of  Nal. 

N 
Assuming  that  33.4  cc.  of  --  AgNO3  V.  S.  were  re- 

quired, each  representing  0014953  gm.  of    Nal,  then 
the  quantity  tested  contained 

33.4  X  0.014953  gm.  or  0.4994302  gm. 


0.49943Q2  X  IPO  8v 

0.5 

The  U.  S.  P.  requirement  is  that  the  salt  contain 
at  least,  of  pure  Nal. 


108      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 


Strontium  Iodide,  Sri,  +  6H2O  =  \  ^1'12.~  0.3 

(    44^-3 

gm.  of  strontium  iodide,  rendered  anhydrous  before 
being  weighed,  is  dissolved  in  10  cc.  of  water,  3  drops 
of  potassium  dichromate  T.  S.  are  then  added,  and  the 

N 

—  AgNO3  V.  S.  run  in    from  a  burette  until  a  perma- 

nent red  coloration  is  produced. 
Apply  the  following  equation  : 

SrI2  +  6H20  +  2  AgN03  =  2  Agl  +  Sr  (NO3)2  +  6H2O. 
2)448.12  2)339.4 

10)224.06  10)169.7  M 

22.406  gms.  16.97  gms.  or  1000  cc.   —  AgNO3  V.  S. 

-      N 
This  equation  shows  that  each  cc.  of  the   —  AgNO3 

V.  S.  represents  0.022406  gm.  of  Srla. 
Zinc  Iodide,  ZnI2  =  j  ^  jg'1  .  —  Dissolve  0.5  gm.  of 

dry  zinc  iodide  in  10  cc.  of  water,  add  2  drops  of  po- 
tassium chromate  T.  S.,  and  then  run  into  the  mixture 

N 
from  a  burette    —  AgNO3V.  S.  until  a  permanent  red 

color  is  produced,  indicating  that  all  of  the  iodide  has 
been  precipitated  in  the  form  of  silver  iodide.  Each  cc. 

N 
of  the  —  silver  solution  used  represents  0.015908  gm. 

of  zinc  iodide. 

ZnI2  +  2AgN03  =  2  Agl  +  Zn(N03)a. 

2)31^.16        2)339.4 
10)159.08      10)169.7  N 

15.908  gms.   16.97  gms.  oriooocc.  —  AgNO3  V.  S. 


A  TEXT- BOOK   OF   VOLUMETRIC   ANALYSIS.       109 

The  U.  S.  P.  directs  that  not  less  than  31   cc.   nor 

N 
more  than  31.4  cc.  of  —  AgNO3  V.  S.  be  required  to 

produce  the  desired  result,  31  cc.  corresponding  to 
98.62$  and  31.4  cc.  to  99.9$  of  pure  zinc  iodide. 

0.015908  X  31.4  =  0.4995112  gm.  of  ZnI3. 
Then 

.    •:     :   0.4995112x100^ 

Ammonium    Chloride,    NH4C1  =  j  *H'f-— It    is 

estimated  in  the  same  manner  as  the  other  soluble  haloid 
salts.  A  weighed  quantity  of  the  salt  is  dissolved  in  a 
small  quantity  of  water  and  the  solution  titrated  with 

-    silver-nitrate  solution  until  no  more  precipitation 

takes  place,  or,  if  potassium  chromate  T.  S.  has  been 
added  as  indicator,  until  a  red  color  makes  its  appear- 
ance. 

NH4C1  +  AgN03  =  AgCl  +  NH4N03. 
10)53.38        10)169.7  N 

5.338  gms.     16.97  gms.  or  1000  cc.  —  V.  S. 

N 
Thus  each  cc.  of  —  V.  S.   used   represents  0.005338 

gm.  of  NH4C1. 
Potassium  Chloride,  KC1  =  j  ^4-40__Thisisesti_ 

mated  in  the  same  manner  as  the.  above,  applying  the 
following  equation  : 

KC1  +  AgN03  =  AgCl  +  KNO3 . 

io)74-4  10)169.7  N 

7.44  gms.      16.97  gms.  or  looocc.  —  AgNO3  V.  S. 


1 10       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

N 
Thus  each  cc.  of   —  V.  S.  represents  0.00744  gm.  of 

KC1. 
Sodium   Chloride,  NaCl  =   j  Jg'37.— A  weighed 

quantity  of  the  well-dried  salt,  say  0.2  gm.,  is  dissolved 
in  about  10  cc.  of  water  and  the  solution  mixed  with 

N 
a  few  drops  of  potassium  chromate  T.   S.     Then  : 

AgNO,  V.  S.  is  run  in  from  a  burette  until  all  the 
chloride  is  precipitated  and  a  permanent  red  color  of 
silver  chromate  is  produced. 

The  U.  S.  P.  directs  that  0.195  gm.  of  the  salt  should 

N 

require  not  less  than  33.4  cc.  of  —  AgNO3  V.  S.  to  pro- 
duce this  reaction. 

The  following  equation  shows  the  reaction  which 
takes  place  between  the  sodium  chloride  and  the  silver 
nitrate : 

NaCl  +  AgN03  =  AgCl  +  NaNO3. 

10)58.37       10)169.7  ^ 

5.837  gms.    16.97  gms.  or  looocc.  —  AgNO3  V.  S. 

Each  cc.  of  the  standard  solution  thus  represents 
0.005837  gm.  of  NaCl. 

•005837  X  33-4  =  0.194958  gm.  of  NaCl. 
0.194958^000  = 
0.195 

Zinc  Chloride,  ZnCl.  -  {  *\lffi- -This  salt  is 
tested  in  exactly  the  same  way  as  the  other  haloid 
salts. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       Ill 

Dissolve  0.3  gm.  of  the  dry  salt  in  about   10  cc.  of 
water,  add  a  few  drops  (2  drops)  of  potassium  chromate 

N 
T.  S.,  and  then  run  into  the  mixture  from  a  burette,  — 

AgNO3  V.  S.  until  a  permanent  red  color  is  produced. 

It  should  require  44.1  cc.  of  the  standard  silver  solu- 
tion to  produce  this  result. 

The  reaction  is  shown  by  the  following  equation  : 

ZnCl,   +    2AgN03  =  2AgCl  +  Zn(NO8)2. 
2)135.84  2)339.4 

io)  67.92  10)169.7 

6.792  gms.        16.97  gms.  or  1000  cc.  —  V.  S. 

N 
Thus  it  is  seen  that  each  cc.  of  the  -  AgNO3  V.  S. 

represents  0.006792  gm.  of  ZnCl2. 

0.006792  X  44-i  =  0.2995272  gm. 

0.2995272  X  IPO 

— —  =  99.84$ 


The  U.  S.  P.  requires  99.! 

Syrupus  Acidi  Hydriodici,  a  syrupy  liquid  contain- 
ing about  ij>  of  HI  U.  S.  P.  HI  =  |  ^7-53.— Oper- 
ate upon  15  grammes.  The  reaction  which  occurs  is 
as  follows  : 

HI     +     AgN03  =  Agl  +  HN03. 
10)127.5  10)169.7  N 

12.75  gms-          J6.97  gms.  or  1000  cc.  -  AgNO3  V.  S. 

The  end  of  the  reaction  is  shown  by  the  cessation 
of  the  formation  of  a  precipitate. 


112       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

Since  nitric  acid  is  liberated,  potassium  chromate  is 
not  admissible  as  indicator. 

The  U.  S.  P.  directs  that  the  syrup  be  neutralized 
by  ammonia  water  before  titration.  This  prevents 
the  formation  of  nitric  acid,  and  admits  of  the  use  of 
potassium  chromate  as  indicator. 

(31.875)  *32  gms.  of  the  syrup,  neutralized,  and 
mixed  with  2  drops  of  the  indicator,  should  require  25 
cc.  of  decinormal  silver-nitrate  solution  to  produce  a 
permanent  red  tint. 

Each  cc.  represents  0.01275  gm.  of  HI. 

0.01275  X  25  =0.31875  gm. 
0.31875  X  IPO          . 
31.875" 

Syrupus  Ferri  lodidi,  a  syrup  containing  about 
10$  by  weight  of  ferrous  iodide  (FeI2)  U.  S.  P.  FeI2  = 

j  #3™94. — Take  2  gms.  of  the  syrup,  mix  it  with  a 

N 

small  quantity  of  water,  and  run  in  the  —  silver  solu- 
tion. The  close  of  the  reaction  is  shown  by  the  cessa- 
tion of  the  formation  of  a  precipitate.  Potassium 
chromate  is  not  admissible  as  an  indicator  in  this  case. 

FeI2   +    2AgN03  -  2AgI  +  Fe(NO3),. 
2)308.94  2)339.4 

10)154.47          10)169.7  N 

15.447  gms.         16.97  gms.  or  1000  cc.  —  V.  S. 

TO 

Thus  each  cc.  represents  0.015447  gm.  of  ferrous 
iodide. 

The  U.  S.  P.  method  originated  with  Volhard.  It 
has  the  advantage  over  the  direct  method  for  haloids 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.     113 

with  chromate  indicator,  in  that  it  may  be  used  in  the 
presence  of  nitric  acid.  It  thus  enables  the  haloids  to 
be  estimated  in  the  presence  of  a  phosphate  or  other 
salt  which  precipitates  silver  in  a  neutral,  but  not  in  an 
acid  solution. 

It  depends  upon  entirely  precipitating  the  chloride, 
in  the  presence  of  nitric  acid,  by  a  known  excess  of 
standard  solution  of  silver  nitrate,  and  then  estimating 
the  excess  of  silver  left  uncombined,  by  the  aid  of  a 
standard  solution  of  potassium  sulphocyanate,  using 
ferric  alum  as  an  indicator. 

The  sulphocyanate  has  a  greater  affinity  for  silver 
than  it  has  for  iron,  and  therefore  so  long  as  any 
silver  is  in  solution,  the  sulphocyanate  will  combine 
with  it  and  form  a  precipitate  of  silver  sulphocyanate. 

As  soon  as  the  silver  is  all  taken  up,  the  sulphocya- 
nate will  combine  with  the  ferric  alum  and  strike  a 
brownish-red  color. 

The  sulphocyanate  solution  is  to  be  made  of  such 
strength  that  it  corresponds  with  the  silver  solution, 
volume  for  volume. 

The  difference  between  the  volume  of  silver  solu- 
tion originally  added,  and  the  volume  of  sulphocyanate 
solution  used,  will  give  the  volume  of  silver  solution 
equivalent  to  the  haloid  salt  present. 

Decinormal  Potassium  Sulphocyanate  V.  S.  (Vol- 

hard's  Solution),  KSCN  =  \  #9&99  '     9^99  1  gms.  in 

(  *97          *9-7      )  * 

I  litre. — Dissolve   10  gms.  of  pure  crystallized   potas- 
sium sulphocyanate  (thiocyanate)  in  1000  cc.  of  water. 
This  solution,  which  is   too  concentrated,  must  be 
adjusted  so  as  to  correspond  in  strength  exactly  with 
decinormal  silver  nitrate  V.  S.     For  this  purpose   in- 


114       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

N 
troduce  into  a  flask  10  cc.  of  —  AgNO3  V.  S.,  0.5  cc. 

of  ammonio-ferric  sulphate  T.  S.,  and  5  cc.  of  diluted 
nitric  acid. 

Run  into  this  mixture  from  a  burette  the  sulphocya- 
nate  solution. 

At  first  a  white  precipitate  of  silver  sulphocyanate 
is  produced,  giving  the  fluid  a  milky  appearance,  and 
then,  as  each  drop  of  sulphocyanate  falls  in,  it  is  sur- 
rounded by  a  deep  brownish-red  cloud  of  ferric  sulpho- 
cyanate, which  quickly  disappears  on  shaking,  as  long 
as  any  of  the  silver  nitrate  remains  unchanged. 

When  the  point  of  saturation  is  reached  and  the 
silver  has  all  been  precipitated,  a  single  drop  of  the 
sulphocyanate  solution  produces  a  faint  brownish-red 
color,  which  does  not  disappear  on  shaking. 

Note  the  number  of  cc.  of  the  sulphocyanate  solu- 
tion used,  and  dilute  the  whole  of  the  remaining 
solution  so  that  equal  volumes  of  this  and  of  the 
decinormal  silver  nitrate  V.  S.  will  be  required  to  pro- 
duce the  permanent  brownish-red  tint.  (The  same 
tint  of  brown  or  red  to  which  the  volumetric  solution 
is  adjusted  must  be  attained  when  the  solution  is  used 
in  volumetric  testing.) 

Assuming  that  9.5  cc.  of  the  sulphocyanate  solution 
were  required  to  produce  the  reaction,  then  each  9.5 
cc.  must  be  diluted  to  make  10  cc.,  or  the  whole  of  the 
remaining  solution  in  the  same  proportion. 

Always  make  a  new  trial  after  the  dilution  to  see  if 
the  solutions  correspond. 

The  U.  S.  P.  method  for  estimating  syrup  of  ferrous 
iodide  is  as  follows : 

1.5447  gms.  (*i.55  gms.)  of  the  syrup  and   10  cc.  of 


A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.       11$ 

water  are  introduced  into  a  flask,  1 1  cc.  of  decinormal 
silver  nitrate  V.  S.  are  added,  then  5  cc.  of  diluted 
nitric  acid,  and  5  cc.  of  ferric  ammonium  sulphate  T.  S. 
The  decinormal  potassium  sulphocyanate  V.  S.  is  now 
run  into  the  mixture  from  a  burette  until  a  reddish- 
brown  tint  is  produced,  which  does  not  disappear  upon 
shaking.  Not  more  than  I  cc.  should  be  required. 

This  corresponds  to  10$  of  ferrous  iodide.  The  re- 
actions which  take  place  are  shown  by  the  following 
equations: 

Pel,  +  2AgNOs  =  2AgI  +  Fe(NO3),;      .    (i) 

15.447  gms.   16.97  gms.  or  1000  cc.  — AgNO3  V.  S. 


10 


AgN03  +  KSCN  =  AgSCN  +  KNO3 ;    .     (2) 

16.97  gms.      9.699 gms.  or  1000  cc.  — KSCN  V.  S. 


Fe,(NH4),(S04)4- 

=  Fe2(SCN)6  +  (NH4)3S04  +  3K2SO,     (3) 

The  Fea(SCN)6  gives  the  brownish-red  color  to  the 
solution. 

The  object  of  the  nitric  acid  is  to  acidulate  the  solu- 
tion, facilitate  the  precipitation  of  the  silver,  and  to 
oxidize  the  ferrous  nitrate. 

In  the  above  case  1 1  cc.  of  silver  nitrate  are  originally 
added.  If  I  cc.  of  potassium  sulphocyanate  be  re- 
quired, it  shows  that  I  cc.  of  the  silver-nitrate  solution 
was  in  excess,  and  that  10  cc.  went  into  combination 
with  the  ferrous  iodide.  The  equation  shows  us  that 


Il6       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

each  cc.  of  silver  nitrate  V.  S.  represents  0.015447  gm. 
of  ferrous  iodide  ;  then  10  cc.  represent 

0.015447  X  10  =  0.15447  gm., 


and     -1544^X200 
1-5447 


of  FeI3  in  the  U.  S.  P.  syrup. 

Saccharated  Ferrous  Iodide. — The  process  for 
estimating  this  compound  is  exactly  the  same  as  that 
for  syrup  of  ferrous  iodide. 

1.5447  gms.  (*i.55  gms.)  of  the  saccharated  ferrous 
iodide  are  dissolved  in  about  20  cc.  of  water  in  a  small 
flask,  and  to  this  solution  is  added  first  22  cc.  of 

N 

—  AgNO3  V.  S.,  then  5  cc.  of  diluted  nitric  acid,  and 

N 
5    cc.  of   ferric   ammonium    sulphate   T.   S.     The   — 

KSCN  V.  S.  is  then  run  in,  from  a  burette,  until  the 
reddish-brown  color  of  ferric  sulphocyanate  is  produced. 

N 
Not  more  than  2  cc.  of  the  —  KSCN  V.  S.  should  be 

required. 

This  corresponds  to  20%  of  pure  ferrous  iodide. 

N 

22  cc.  of  —  silver  nitrate 
10 

N 
—  2  cc.  of  —  potassium  sulphocyanate 

N 

=  20  cc.  of  —  silver  nitrate, 
10 


A  TEXT-BOOK    OF  VOLUMETRIC   ANALYSIS.       1  17 
which  reacted  with  the  ferrous  iodide,  then 

0.015447  X  20  =  0.30894  gm., 

0.30894  X  IPO  _ 

1-5447 

Syrup  of  Ferrous  Bromide,  U.  S.  P.  1880,  FeBr2  = 
*4.  —  This   syrup    may    be    tested    in    the   same 


manner  as  the  syrup  of  ferrous  iodide,  either  by  the 
direct  method,  using  the  cessation  of  precipitation  as 
the  end  reaction,  or  by  the  residual  method  with 
potassium  sulpho-  cyanate. 

The  factor  is  0.01077. 

Hydrocyanic  Acid,    HCN  =  j  ^6.9^_Dilute   hy_ 

drocyani  cacid  may  be  estimated  by  weighing  out  about 
5  gms.,  and  adding  to  this  sufficient  soda  or  potassa 
solution  to  convert  the  acid  into  sodium  or  potassium 
cyanide  (NaCN  or  KCN),  and  leave  the  solution 
strongly  alkaline. 

To  this  solution  is  added  the  decinormal  silver- 
nitrate  solution  until  a  permanent  turbidity  occurs. 

This  turbidity  is  due  to  the  precipitation  of  silver 
cyanide,  and  affords  a  delicate  proof  of  the  completion 
of  the  reaction. 

The  difficulty  experienced  in  this  process  is  in  the 
conversion  of  the  acid  into  the  cyanide.  The  sodium 
cyanide  has  a  strong  alkaline  reaction,  turning  litmus 
blue  when  only  a  small  proportion  of  the  acid  has  been 
neutralized. 

If  the  titration  is  conducted  before  the  acid  is  com- 
pletely neutralized,  that  which  is  free  will  not  be  acted 


Il8       A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

upon.  Indeed,  cyanide  of  sodium  may  be  estimated  in 
the  presence  of  hydrocyanic  acid  in  this  way. 

According  to  Senier,  the  following  procedure  will 
answer  well  : 

To  the  dilute  hydrocyanic  acid  add  soda  solution  to 
a  strong  alkaline  reaction,  determined  by  litmus  tinc- 

N 

ture.     Then  titrate  with  -  -   silver  nitrate  V.  S.,  drop 

10 

by  drop,  from  the  burette.  If  the  liquid  becomes 
acid,  add  a  little  more  soda  solution  to  bring  it  back  to 
alkalinity,  and  continue  the  titration  until  the  turbidity 
indicates  the  end  of  the  reaction.  The  liquid  must  be 
kept  alkaline  throughout  the  process.  It  is  not  well  to 
add  too  much  soda  solution  at  the  beginning,  as  this 
would  use  up  too  much  of  the  silver  solution,  and  make 
the  reading  a  trifle  too  high. 

The  following  equations,  etc.,  explain  the  reactions : 

2HCN  +  2NaOH  =  2NaCN  +  2H2O  ; 
10)53.96  10)97.96 

5.396  gms.  9.796  gms. 

2NaCN  +  AgNO,  =  AgCN,NaCN  +  NaNO3. 
10)97.6          10)169.7  N 

9.796  gms.      16.97  gms.  or  1000  cc.  —  V.  S. 

It  is  seen  that  5.396  gms.  of  real  HCN  are  equivalent 
to  9.796  gms.  of  sodium  cyanide,  and  represent  16.97 

N 
gms.  of  silver  nitrate,  or  looocc.  of  the  —  V.  S.     That 

-  N 
is,  1000  cc.  of  the  —  AgNO3  V.  S.  may  be  added  to  a 

solution  containing  9.796  gms.  of  sodium  cyanide,  and 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       I  IQ 

no  precipitate  be  produced ;  but  if  one  or  two  drops 
more  of  the  standard  solution  be  added,  a  precipitate 
is  at  once  formed. 

N 
Each  cc.  of  —  AgNO3  V.  S.,  which  fails  to  produce 

a  precipitate  with  a  solution  of  sodium  cyanide,  repre- 
sents 0.009796  gm.  of  NaCN,  which  is  equivalent  to 
.005396  gm.  of  HCN. 

With  2  molecular  weights  of  sodium  or  potassium 
cyanide,  one  molecule  of  silver  nitrate  forms  a  double 
salt,  having  the  composition  NaCN,AgCN,  and  which 
is  soluble. 

When  more  silver-nitrate  solution  is  added,  this  solu- 
ble double  salt  is  decomposed,  and  a  precipitate  of 
silver  cyanide  occurs,  thus: 


AgCN,NaCN  +  AgNO3  =  2AgCN  +  NaNO3. 

The  U.  S.  P.  method  is  as  follows : 

A  weighed  quantity  of  the  acid  is  mixed  with  suffi- 
cient of  an  aqueous  suspension  of  magnesia  to  make 
an  opaque  and  decidedly  alkaline  mixture. 

To  this  a  few  drops  of  potassium  chromate  T.  S.  are 

N 
added,  and  the      -   silver   solution    delivered    from    a 

burette  until  the  red  color  of  silver  chromate  appears. 
1.35  gms.  of  the  diluted  acid  is  mixed  with  enough 
water  and  magnesia  to  make  an  opaque  mixture  of 
about  10  cc.  Add  to  this  2  or  3  drops  of  potassium 
chromate  T.  S.,  and  then  from  a  burette  deliver  the 
decinormal  silver  nitrate  V.  S.  until  a  red  tint  is  pro- 
duced which  does  not  again  disappear  by  shaking. 


120      A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

Each  cc.  of  the  standard  silver  solution  used,  repre- 
sents 0.002698  gm.  of  absolute  HCN. 

HCN  +  AgNO3  =  AgCN  +  HNO3. 
10)26.98        10)169.7 

2.698  gms.      16.97  gms.  or  1000 cc.  —  silver  nitrate  V.  S. 

10 

Potassium  Cyanide,   KCN  =   j  *£>'°1.— This  salt 

may  be  estimated  in  the  following  manner  : 

I  gm.  of  the  salt  is  dissolved  in  sufficient  water,  and 

into  the   solution,  is  delivered   in   drops  the   standard 

silver  solution  until  a  precipitate  appears  which  is  not 

redissolved  on  agitation. 

If  0.65  gm.  of  KCN  are  taken,  not  less  than  45  cc.  of 

N 

-Q  AgNO3  V.  S.  should  be  required. 

2KCN  +  AgNO3  =  AgCN,KCN  +  KNO3 . 
10)130.02       10)169.7 

13.002  gms.     16.97  gms.  or  1000  cc.  —  AgNO3  V.  S. 

Thus  each  cc.  of  the  standard  silver  solution  repre- 
sents 0.013  gm-  °f  KCN. 

0.013  X  45  =  0-585  gm. 
.585  X  IPO  _ 
.65 

Cyanides  maybe  estimated  also  by  iodine,  according 
to  Fordos  and  Gelis. 

This  process  depends  upon  the  fact  that  potassium 
cyanide  decolorizes  iodine,  potassium  iodide  and 
cyanogen  iodide  being  formed. 

When  iodine  solution   is  added  to  a  solution  of  po- 


A  TEXT-BOOK    OF  VOLUMETRIC  ANALYSIS.       121 

tassium  cyanide,  the  iodine  is  decolorized  as  long  as 
there  is  any  undecomposed  cyanide  present. 
The  following  equation  expresses  the  reaction 

KCN     +     I2    =    KI  +  CNI, 

2)65.01  2)153.06 

10)32.505        10)126.53  N 

3.2505  gms.     12.653  gms-  or  I00°  cc-  —  iodine  V.  S. 

Thus  each  cc.  of  the  volumetric  solution  represents 
0.00325  gm.  of  KCN. 

The  end  of  the  reaction  is  known  by  the  yellow  color 
of  the  iodine  solution  becoming  permanent. 

Silver  Nitrate,  (Argenti  Nitras)  AgNO3=  j  *|^;*5. 

— Nitrate  of  silver  and  other  salts  of  this  metal  may 
be  volumetrically  estimated  by  standard  solution  of 
sodium  chloride. 

The  silver  salt  is  dissolved  in  sufficient  water  in  a 
beaker,  and  a  decinormal  volumetric  solution  of  sodium 
chloride  run  in  until  a  precipitate  is  no  longer  pro- 
duced. 

The  estimation  may  also  be  performed  by  retitration 
as  follows  : 

To  the  silver  solution  contained  in  a  beaker  add  a 

N 

measured  excess  of  --   sodium  chloride  V.  S.,  and  then, 
10 

after  adding  a  few  drops  of  potassium  chromate  T.  S., 

N 

titrate  the  mixture  with  —  silver  nitrate  V.  S.  until  a 

10 

permanent  red  color  appears.  Deduct  the  number  of 
cc.  of  silver  nitrate  V.  S.  from  the  quantity  of  sodium 
chloride  V.  S.  and  the  quantity  of  the  latter  is  ob- 
tained which  actually  combined  with  the  silver  solution 
under  examination. 


122       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

The  sulphocyanate  method  of  Volhard  may  also  be 
employed  in  the  estimation  of  silver. 

^    Sodium    Chloride   V.    S.,    NaCl  =   \    *l'M. 
10  (    55.4 

»5*o-      r  gms.  in  I  litre. — Dissolve   5.837  gms.  of  pure 

sodium  chloride  in  enough  water  to  make  exactly 
1000  cc.  at  the  ordinary  temperature  of  the  atmos- 
phere. 

Check  this  solution  with  decinormal  silver  nitrate 
V.  S.  The  two  solutions  should  correspond,  volume 
for  volume. 

Pure  Sodium  Chloride  may  be  prepared  by  passing 
into  a  saturated  aqueous  solution  of  the  purest  com- 
mercial chloride  of  sodium  a  current  of  dry  hydro- 
chloric-acid gas.  The  crystalline  precipitate  is  then 
separated  and  dried  at  a  temperature  sufficiently  high 
to  expel  all  traces  of  free  acid. 

The  U.  S.  P.  method  for  silver  nitrate  is  as  follows  : 

*O.34gm.  (0.3391  gm.)  of  silver  nitrate  is  dissolved  in 
10  cc.  of  distilled  water,  and  the  solution  carefully 

N 
titrated  with  —  NaCl  V.  S.  until  precipitation  ceases. 

20  cc.  of  the  standard  solution  should  be  required. 

AgNO,    +    NaCl  =  AgCl  +  NaNO3. 
10)169.55*         10)58.37  N 

J6.955  gms.         5. 837  gms.  or  looocc.  —  NaCl  V.  S. 

Each  cc.  of  the  standard  solution  represents  0.01695 5 
gm.  of  pure  AgNO3. 

0.016955  X  20  =  0.3391  gm. 

0.3391  X  ioo  , 

°°^  -  —  100$ 

•3391 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       123 

Argenti  Nitras  Dilutus   (Mitigated  Caustic). — This 
may  be  estimated  in  the  same  manner  as  the  above. 
The  U.  S.  P.  method  is  as  follows : 
I  gm.  is  dissolved  in  10  cc.  of  distilled  water,  to  this 

N 
is  added  20  cc.  of  —  NaCl  V.  S.  and  a  few  drops  of 

N 
potassium  chromate  T.  S.,  and  the  excess  of  —  NaCl 

N 
V.  S.  found  by  titration  with  —  AgNO3  V.  S.  until  a 

permanent  red  color  is  produced.     Not  more  than  0.5 
cc.  of  the  latter  should   be  required.     This  indicates 

N 
that  19.5  cc.  of  —   NaCl  V.  S.  were  actually  required 

to  completely  precipitate  the  silver  nitrate  tested. 
Therefore 

0.016955  x  19.5  =  -3306225  gm- 


Argenti  Nitras  Fusus  (Moulded  Silver  Nitrate. 
Lunar  Caustic). — This  is  treated  in  exactly  the  same 
manner  as  the  above.  0.34  gm.  of  the  lunar  caustic  is 
dissolved  in  water,  and  20  cc.  of  standard  sodium 
chloride  added  ;  not  more  than  I  cc.  of  this  should  be 
in  excess,  as  shown  by  retitration  with  silver  nitrate 
V.  S.,  using  chromate  indicator. 

This  corresponds  to  about  95$  of  pure  silver  nitrate. 

Silver  Oxide,  Ag,O  =  231.28. — May  be  converted 
into  nitrate  by  solution  in  nitric  acid,  and  then  test- 
ing as  above  for  silver  nitrate.  There  will  prob- 
ably be  some  free  nitric  acid  present  if  this  is  done, 


124       A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

and   therefore   the  sulphocyanate   method  is  best   em- 
ployed. 

The  Sulphocyanate  Method.  —  A  weighed  quantity 
of  the  silver  salt  is  dissolved  in  water,  some  diluted 
nitric  acid  and  ammonium  ferric  sulphate  solution  are 

N 

added,  and  the  mixture  then  titrated  with  —  potassium 

10 

sulphocyanate  V.  S.  until  a  permanent  reddish-brown 
color  of  feric  sulphocyanate  is  produced. 

The  following  equation  explains  the  reactions  : 

AgN03  +  KSCN  =  AgSCN  +  KNO3. 

10)169.55  10)96.99 

16.955  g™s.      9.699  gms.  or  1000  cc.  standard  V.  S. 

Thus  each  cc.  of  the  standard  V.  S.  represents 
0.016955  gm.  of  pure  silver  nitrate,  or  0.010766  gm.  of 
metallic  silver. 

Liquor  Plumbi  Subacetatis  (Goulard's  Extract).  — 
This  is  an  aqueous  solution  containing  about  25$  of 
lead  subacetate,  the  formula  of  which  is  approximately 
Pb3O(C3H3O2)2  =  546.48.  This  is  estimated  by  precipi- 
tation with  sulphuric  acid. 

(13.6622  gms.)*J3.67  gms.  of  the  solution  are  diluted 
with  50  cc.  of  water,  a  few  drops  of  methyl-orange  added, 
and  the  mixture  titrated  with  normal  sulphuric  acid 
until  the  lead  is  completely  precipitated  and  the  mix- 
ture has  assumed  a  red  color.  The  red  color  indicates 
an  acid  reaction.  The  reaction  is  illustrated  by  the 
following  equation  : 


4)546.48  4)196  N 

136.62  gms.      49  gms.  or  1000  cc.    -  H2SO4  V.  S. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       125 

N 
Thus  each  cc.  of  —  HaSO4  V.  S.  represents  0.13662 

gm.  of  the  subacetate. 

If  25  cc.  of  the  standard  solution  are  required,  then 
the  solution  under  analysis  contains  0.13662  X  25  = 
3.4155  gms. 

3.4155  Xioo 
13.662 

The  Diluted  Solution  of  Lead  Subacetate  (Lead 
Water)  may  be  estimated  in  the  same  manner. 


126       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


TABLE  OF  SUBSTANCES  ESTIMATED  BY  PRECIPITATION,  GIVING 
FORMULA,  MOLECULAR  WEIGHT,  STANDARD 
SOLUTION  USED,  AND  FACTOR. 


Name. 

Formula. 

Molec- 
ular 
weight. 

Standard  Solu- 
tion Used. 

Factor. 

Acid  hydrobromic 

HBr 

80.76 

—  AgNO3 

0.008076 

IO 

"    hydrocyanic  

HCN 

26.98 

IA.NO, 

0.002698 

"    hydriodic  
Ammonium  bromide  
"           chloride  

HI 
NH4Br 
NH4C1 

127.53 
97-77 
53.38 

tt 

0.01275 
0.009777 
0.005338 

"           iodide  
Calcium  bromide 

NH4I 
CaBrQ 

M4-54 

" 

0.014454 
0.0099715 

"        chloride  

CaCl2 

J99-43 
110.65 

« 

0.005532 

Ferrous  bromide  

FeBr2 

215.40 

" 

0.01077 

"       iodide  

F  I 

tr&  CIA 

—  AgNO3  and 

0.015447 

e  2 

300.94 

IO 

10 

Lead  acetate  .  

Pb(CaH,OaVlHaO 

378.0 

^  H2S04 

0.189 

"    subacetate  

Pb20(C2H302)a 

546.48 

" 

0.13662 

Lithium  bromide  

LiBr 

86.77 

-AgNO, 

IO 

0.008677 

Potassium  bromide  

KBr 

118.79 

0.011879 

chloride  
cyanide  

KC1 
KCN 

74-40 
65.01 

u 

0.00744 
0.01300 

"           iodide  

KI 

165.56 

ifc 

0.016556 

"          sulphocyanide 

KSCN 

96.99 

4* 

0.009699 

Silver  (metallic)  

Agu 

215.32 

-  NaCl  or 

0.010766 

10 

-KSCN 

IO 

"      nitrate  

AgNOa 

I  6O      ^ 

l< 

fiocc 

"      oxide  

•**•&  M  ^3 

Ag20 

231.28 

M 

0.011564 

Sodium  bromide  

NaBr 

102.76 

—  AgNO3 

0.010276 

"      chloride,  

NaCl 

58.37 

10     » 

0.005837 

"       iodide  

Nal 

Strontium  bromide  
iodide  

SrBr2.6H2O 
SrI2.6H2O 

149-53 
354-58 

" 

0.014953 

0.012341 

Zinc  bromide  

ZnBr2 

44  .1 

14 

^° 

fci    chloride                  ... 

ZnClo 

224-   2 

M 

o.oi  1231 

"    iodide  

ZnI2 

I35-°4 
318.16 

it 

o.oo  792 

A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       127 


CHAPTER   XI. 
OXIDIMETRY— ANALYSIS   BY   OXIDATION. 

AN  extensive  series  of  analyses  are  made  by  this 
method,  with  extremely  accurate  results — in  fact,  the 
results  are  generally  more  accurate  than  any  which  can 
be  obtained  by  weighing. 

The  principle  involved  in  this  method  is  extremely 
simple. 

Substances  which  are  capable  of  absorbing  oxygen 
or  are  susceptible  of  an  equivalent  action  are  subjected 
to  the  action  of  an  oxidizing  agent  of  known  power, 
and  the  quantity  of  the  latter  required  for  complete 
oxidation  ascertained. 

The  substances  which  are  used  as  oxidizing  agents 
in  volumetric  analysis  are  potassium  dichromate,  po- 
tassium permanganate,  iodine,  etc. 

The  reducing  agents,  or  deoxidizers,  are  sodium  thio- 
sulphate,  oxalic  acid,  arsenous  oxide,  stannous  chloride, 
metallic  zinc,  and  magnesium. 

Thus  ferrous  oxide  (FeO),  an  oxidizable  substance, 
is  ever  ready  and  willing  to  take  up  oxygen,  while 
potassium  dichromate  and  permanganate  are  always 
ready  to  give  up  some  of  their  oxygen.  .When  po- 
tassium permanganate  gives  up  its  oxygen  in  this  way 
it  loses  its  color,  and  in  volumetric  analysis  advantage 
is  taken  of  this  fact.  When  the  permanganate,  which 
is  added  in  drops  from  a  burette,  is  no  longer  decolor- 


128       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

ized,  the  iron  salt  is  completely  oxidized.     The  reac- 
tion is  as  follows : 

roFeO  +  2KMnO4  =  5Fe2O3  +  2MnO  +  K2O. 

Ferrous  oxide.  Ferric  oxide. 

The  oxidation  of  ferrous  oxide  by  potassium  dichro- 
mate  is  shown  by  the  following  equation  : 

6FeO  +  K2Cr207  =  3Fe2O3  +  Cr2O3  +  K2O. 

An  oxidation  is  always  accompanied  by  a  reduction, 
the  oxidizing  agent  being  itself  reduced  in  the  opera- 
tion. As  seen  in  the  above  equations,  the  manganic 
compound  is  reduced  to  a  manganous  compound,  and 
the  chromic  to  a  chromous  compound. 


ESTIMATION   OF   FERROUS   SALTS. 

Ferrous  salts  are  estimated  by  oxidizing  them  either 
with  potassium  dichromate  or  potassium  perman- 
ganate. 

In  some  respects  the  dichromate  possesses  advan- 
tages over  permanganate. 

1.  It  may  be  obtained  in  a  pure  state. 

2.  Its  solution  does  not  deteriorate  upon  standing  as 
does  that  of  permanganate. 

3.  It  is  not  decomposed  by  contact  with  rubber  as 
the   permanganate  is,  and   may  therefore  be  used    in 
Mohr's  burette.     Its   great  disadvantage,  however,  is 
that  when  used  in  the  estimation  of  ferrous  salts  the 
end  reaction  can  only  be  found  by  using  an  external 
indicator.     The  indicator  which  must  be  used  is  freshly 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

prepared  potassium  ferricyanide  T.  S.,  a  drop  of 
which  is  brought  in  contact  with  a  drop  of  the  solution 
being  tested,  on  a  white  slab,  at  intervals  during  the 
titration,  the  end  of  the  reaction  being  the  cessation  of 
the  production  of  a  blue  color,  when  the  two  liquids 
are  brought  together.  Thus  the  estimation  by  potas- 
sium dichromate  is  cumbersome,  and  very  exact  results 
are  not  easily  obtained. 

If  potassium-permanganate  solution  is  used  for  the 
estimation  of  these  salts  the  end  of  the  reaction  is 
easily  found  without  the  use  of  an  indicator. 

The  permanganate  is  decomposed  the  instant  it  is 
brought  in  contact  with  a  ferrous  salt  in  an  acid  solu- 
tion ;  therefore  as  long  as  any  ferrous  salt  remains  in 
solution  the  permanganate  is  decolorized,  and  when  it 
ceases  to  lose  its  color  the  reaction  is  complete. 

Preparation    of  Standard   Solution   Decinormal 

Potassium  Dichromate  V.  S.,  K3Cr2O7  =  j  ^93 7^ 

*4*Q      [  £ms'  *n  l  ^tre- — 4"896  gms.  (*4-9gms.)  of  pure 

potassium  dichromate  are  dissolved  in  sufficient  water 
to  make,  at  the  ordinary  temperature  of  the  atmos- 
phere, exactly  1000  cc. 

Pure  Potassium  Dichromate  for  use  in  volumetric 
analysis  should  respond  to  all  the  tests  for  purity  given 
in  the  text  of  the  U.  S.  P.  (under  Potassii  Dichromate}, 
as  well  as  to  the  following:  A  solution  of  0.5  gm.  of 
the  salt  in  10  cc.  of  water,  rendered  acid  by  0.5  cc.  of 
nitric  acid,  should  produce  no  visible  change  when 
treated  with  barium  chloride  T.  S.  (absence  of  sulphate), 
nor  with  silver  nitrate  T.  S.  (absence  of  chloride). 

If  a  mixture  of  10  cc.  of  an  aqueous  solution  of  the 


TUTITBRSITT' 


130      A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

salt  (1-20)  with  I  cc.  of  ammonia  water  be  treated  with 
ammonium  oxalate  T.  S.,  no  precipitate  should  be  pro- 
duced (absence  of  calcium). 

Standard  solution  of  potassium  dichromate  is  some- 
times used  as  a  neutralizing  solution  for  estimating 
alkalies,  phenolphthalein  being  used  as  indicator. 

When  used  for  this  purpose  the  decinormal  solution 
contains  14.689  gms.  in  I  litre  (one  half  the  molecular 
weight  in  grammes).  It  is  then  the  exact  equivalent 
of  any  decinormal  acid  V.  S. 

Decinormal  potassium  dichromate  V.  S.  may  also  be 
used  in  conjunction  with  potassium  iodide  and  sul- 
phuric acid  for  standardizing  sodium  thiosulphate  V.  S. 
Iodine  is  liberated  from  potassium  iodide  in  this  reac- 
tion. The  reaction  is  expressed  by  the  equadon 


=  4K5SO(  +  Cr/SO,),  +  7H,0  +  3!,. 

When  used  as  an  oxidizing  agent  to  convert  ferrous 
into  ferric  salts,  or  to  liberate  iodine  from  potassium 

N 
iodide,  the  —  solution  of  potassium  dichromate  must 

contain  4.689  gms.  in  I  litre.     If  the  decinormal  solution 
containing  14.689  gms.  in  I  litre  is  used,  it  has  the  effect 

3N 

of  a  --  solution. 
10 

The  decinormal  solution  which  is  used  as  an  oxidizing 
agent  is  chemically  equivalent  to  decinormal  potassium 
permanganate.  When  used  for  the  purpose  of  liberating 
iodine  from  potassium  iodide,  it  is  the  equivalent  of  an 
equal  volume  of  decinormal  sodium  thiosulphate. 

For  titrating  ferrous  salts  the  decinormal  solution  of 
dichromate  is  used  in  the  following  manner: 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       131 

Make  an  aqueous  solution  of  the  ferrous  salt,  intro- 
duce it  into  a  flask,  and  acidulate  it  with  sulphuric  or 
hydrochloric  acid.  Now  add  gradually  from  a  burette 
the  decinormal  potassium  dichromate  V.  S.  until  a 
drop  taken  out  upon  a  white  slab  no  longer  shows  "a 
blue  color  with  a  drop  of  freshly  prepared  potassium 
ferricyanide  T.  S.  Note  the  number  of  cc.  of  the 
standard  solution  used,  multiply  this  number  by  the 
factor,  and  thus  obtain  the  quantity  of  pure  salt  in  the 
sample  taken. 

Ferrous  salts  strike  a  blue  color  with  potassium 
ferricyanide  T.  S  ;  but  as  the  quantity  of  ferrous  salts 
gradually  diminishes  during  the  titration,  the  blue  be- 
comes somewhat  turbid,  acquiring  first  a  green,  then  a 
gray,  and  lastly  a  brown  shade.  The  process  is  finished 
when  the  greenish-blue  tint  has  entirely  disappeared. 

The  reaction  of  potassium  dichromate  with  ferrous 
salts  always  takes  place  in  the  presence  of  free  sul- 
phuric or  hydrochloric  acid  at  ordinary  temperatures, 
Nitric  acid  should  not  be  used. 

If  it  is  desired  to  estimate  ferric  salts  by  this  standard 
solution  it  is  necessary  to  first  reduce  them. 

This  may  be  done  by  metallic  zinc,  magnesium,  sul- 
phurous acid,  the  alkali  sulphites,  or  by  stannous 
chloride. 

Standard  potassium  dichromate  may  be  checked  in 
the  same  way  as  standard  permanganate,  with  pure 
metallic  iron,  as  described  below. 

Decinormal    Potassium    Permanganate    V.   S., 

2KMn04  =  |  »^|'34.     It  contains  *3'^34  1  gms.  in  I 

litre. — This  solution  may  be  prepared  by  dissolving  the 
pure  crystals  in  fresh  distilled  water.     If  the  salt  can  be 


132       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


obtained  perfectly  pure  and  dry,  a  decinormal  solution 
will  be  obtained  if  3.1534  gms.  are  dissolved  in  distilled 
water,  sufficient  to  make  looocc.  at  the  ordinary  atmos- 
pheric temperature ;  but  nevertheless  it  is  always  well  to 
verify  it  as  described  below.  The  solution  will  retain 
its  strength  for  several  weeks  if  well  kept,  but  it  should 
always  be  checked  by  titration  before  it  is  used. 

The  standardization  of  permanganate  solution  may 
be  effected  as  follows : 

With  Metallic  Iron — Thin  annealed  binding-wire, 
free  from  rust,  is  one  of  the  purest  forms  of  iron. 

O.I  gm.  of  such  iron  is  placed  in  a  flask  which  is 
provided  with  a  cork  through 
which  a  piece  of  glass  tubing 
passes,  to  the  top  of  which  a 
piece  of  rubber  tubing  is  at- 
tached, which  has  a  vertical  slit 
about  one  inch  long  in  its  side, 
and  which  is  closed  at  its  upper 
end  by  a  piece  of  glass  rod  (see 
Fig.  24).  Diluted  sulphuric  acid 
is  added  and  gentle  heat  ap- 
plied. The  iron  dissolves  and 
the  steam  and  liberated  hy- 
drogen escape  through  the  slit 
under  slight  pressure.  The  air 
is  thus  prevented  from  enter- 
ing and  the  ferrous  solution 
protected  from  oxidation. 

When  the  iron  is  completely  dissolved  a  small  quan- 
tity of  cold,  recently  boiled,  distilled  water  should  be 
added,  and  the  titration  with  potassium  permanganate 
at  once  begun  and  continued  until  a  faint  permanent 


FIG.  24. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       133 

red  color  is  produced.  If  the  solution  is  decinormal, 
exactly  17.85  cc.  will  be  required  to  produce  this 
result. 

The  iron  is  converted  by  the  sulphuric  acid  into 
ferrous  sulphate,  Fe2  +  2H2SO4  '=  2FeSO4  +  2H2. 
This  ferrous  sulphate  is  easily  oxidized  by  the  air,  and 
therefore  it  is  directed  that  access  of  air  should  be 
prevented,  and  the  distilled  water,  with  which  the  solu- 
tion is  diluted,  previously  boiled  in  order  to  drive  off 
any  dissolved  free  oxygen. 


ioFeS04  +  2KMn04  +  8H,SO4 
IO°)5  100)315.34 


N 


_ 

5.588  gms.        3.1534  gms.  or  1000  cc.  —  V.  S. 


=  5Fea(S04)3  +  K3S04  +  2MnS04  +  8H2O. 

N 
This   equation,    etc.,    shows   that   each   cc.    of   — 

2KMnO4  V.  S.  represents  .005588  gm.  of  metallic  iron. 

With  Oxalic  Acid.  —  0.063  gm.  of  the  pure  crystal- 
lized acid  is  weighed  (or  10  cc.  of  decinormal  oxalic  acid 
V.  S.  carefully  measured)  and  placed  in  a  flask,  with 
some  dilute  sulphuric  acid  and  considerable  water,  the 
mixture  warmed  to  about  60°  C.  (140°  F.),  and  the 
permanganate  added  from  a  burette. 

The  action  is  in  this  case  less  decisive  and  rapid 
than*  in  the  titration  with  iron,  and  more  care  should 
be  used.  The  color  disappears  slowly  at  first,  but 
afterwards  more  rapidly. 

Note  the  number  of  cc.  of  the  permanganate  solu- 
tion used,  and  then  dilute  the  remainder  so  that  equal 
volumes  of  decinormal  oxalic  acid  and  decinormal 
permanganate  solution  will  exactly  correspond. 


134      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

Example. — Assuming  that  9  cc.  of  the  perman- 
ganate solution  first  prepared  had  been  required  to 
produce  a  permanent  pink  tint  when  titrated  into  10 

N 
cc.  of  —   oxalic-acid  solution,  then  the  permanganate 

must  be  diluted  in  the  proportion  of  9  of  permanganate 
and  i  of  distilled  water,  or  900  and  100. 

The  U.  S.  P.  gives  the  following  method  for  the 
preparation  of  this  solution  : 

A  stronger  and  a  weaker  solution  is  made  and  mixed 
in  certain  proportions  to  form  a  solution  of  the  proper 
strength.  It  is  said  that  when  thus  prepared  the  solu- 
tion will  keep  its  titre  for  months  if  properly  preserved. 

The  Stronger  Solution. — 3.5  gms.  of  pure  crystallized 
permanganate  are  dissolved  in  1000  cc.  of  water  by 
the  aid  of  heat,  and  the  solution  then  set  aside  in  a 
closed  flask  for  two  days,  so  that  any  suspended  mat- 
ters may  deposit. 

The  Weaker  Solution. — Dissolve  6.6  gms.  of  the  salt 
in  2200  cc.  of  water  in  the  same  manner  as  above,  and 
set  this  solution  aside  for  two  days. 

These  two  solutions  are  then  separately  titrated 
in  the  following  manner: 

Introduce  10  cc.  of  decinormal  oxalic-acid  solution 
into  a  flask,  add  I  cc.  of  pure  concentrated  sulphuric 
acid,  and  before  the  mixture  cools  add  the  perman- 
ganate solution  slowly  from  a  burette,  shaking  the 
flask  after  each  addition,  and  towards  the  end  of  the 
operation  reducing  the  flow  to  drops.  When  the  last 
drop  is  no  longer  decolorized,  but  imparts  a  pinkish 
tint  to  the  liquid,  the  reaction  is  completed.  Note  the 
number  of  cc.  consumed.  Finally,  mix  the  two  solu- 
tions in  such  proportions  that  equal  volumes  of  the 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       135 

N 
mixture  and  of  —  oxalic  acid  V.  S.  will  exactly  corre- 

spond. 

To  obtain  the  accurate  proportions  for  mixing  the 
two  solutions,  deduct  10  from  the  number  of  cc.  of  the 
weaker  solution  consumed  in  the  above  titration  ;  with 
this  difference  multiply  the  number  of  cc.  of  the 
stronger  solution  consumed  :  the  product  shows  the 
number  of  cc.  of  the  stronger  solution  needed  for  the 
mixture. 

Then  deduct  the  number  of  cc.  of  the  stronger  solu- 
tion consumed  in  the  titration  from  10,  and  with  the 
difference  multiply  the  number  of  cc.  of  the  weaker 
solution  consumed  :  the  product  shows  the  number  of 
cc.  of  the  weaker  solution  needed  for  the  mixture. 

Or,  designating  the  number  of  cc.  of  the  stronger  so- 
lution by  S,  and  the  number  of  cc.  of  the  weaker  solu- 
tion by  W,  and  using  the  following  formula,  the 
proportions  in  which  the  solutions  must  be  mixed  are 
obtained: 

Stronger  Solution.  Weaker  Solution. 

(J^--io)S    +    (io 


Example.  —  Assuming  that  9  cc.  of  the  stronger  and 
10.5  cc.  of  weaker  had  been  consumed  in  decomposing 

N 
IO  cc.  of  —  oxalic  acid  V.  S.  ;  then,  substituting  these 

values  in  the  above  formula,  we  obtain 

(10.5  -  10)9  +  (10-9)10.5, 
or  4.5      +  10.5, 

making  15  cc.  of  final  solution. 


136       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

The  bulk  of  the  two  solutions  is  now  mixed  in  the 
same  proportion  :  450  cc.  of  the  stronger  and  1050  cc. 
of  the  weaker,  or  900  cc.  of  the  stronger  and  2100  cc. 
of  the  weaker. 

After  the  solutions  are  thus  mixed  a  new  trial  should 
be  made,  when  10  cc.  of  the  solution  should  exactly 

N 
decompose  10  cc.  of  —  oxalic  acid  V.  S. 

The  reaction  between  potassium  permanganate  and 
oxalic  acid  is  illustrated  by  the  following  equation : 

2KMn04  +  5(H2C204.2H20)  +  sH2SO4  - 

KSSO4  +  2MnSO4  +  ioCOa  +  i8H2O. 


ESTIMATION   OF   FERROUS   SALTS  WITH   POTASSIUM 
BICHROMATE. 

One  molecule  of  potassium  dichromate  yields,  under 
favorable  circumstances,  three  atoms  of  oxygen  for 
oxidizing  purposes.  This  is  shown  by  the  following 
equation  : 

6FeO  +  K.Cr.0,  =  3Fe,O,  +  Cr,O,  +  K,O. 

Here  it  is  seen  that  the  three  liberated  atoms  of 
oxygen  combine  at  once  with  the  ferrous  oxide,  con- 
verting it  into  ferric  oxide  : 

6FeO  +  03  =  Fe609     or     3FeaO3. 

In  the  oxidation  of  a  ferrous  salt,  the  reaction  takes 
place  only  in  the  presence  of  an  acid. 

The  dichromate  then  gives  up  its  oxygen.     Four  of 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       137 

its  oxygen  atoms  combine  at  once  with  the  replaceable 
hydrogen  of  the  accompanying  acid,  the  other  three 
being  liberated.  The  three  oxygen  atoms  thus  set 
free  are  available  either  for  direct  oxidation  or  for 
combination  with  the  hydrogen  of  more  acid.  In  the 
latter  case  a  corresponding  quantity  of  acidulous  radi- 
cals is  set  free. 

The  following  equation  indicates  this  reaction : 

K,Cr.O,  +  4H,S04  =  K.SO,  +  Cr,(SO.).  +  4H,O  +  O,. 

In  this  case  four  of  the  liberated  atoms  of  oxygen 
combine  with  eight  of  the  atoms  of  hydrogen  of  sul- 
phuric acid  and  liberate  four  SO4  radicals,  which  at 
once  combine  with  the  K2  and  Cr2  of  the  dichromate. 
The  other  three  atoms  are  set  free.  If  seven  sulphuric- 
acid  molecules  are  used  instead  of  four  molecules,  the 
three  free  atoms  of  oxygen  will  liberate  3(SO4): 

KaCrA+7H,SO,=K5SO<+Cr,(SO.)s+7H,0  +  (SO.)s. 

If  this  liberation  of  3(SO4)  takes  place  in  the  pres- 
ence of  a  ferrous  salt,  the  3(SO4)  will  combine  with  six 
molecules  of  the  ferrous  salt,  converting  it  into  a  ferric 
salt: 

6FeS04  +  3S04  =  Fe,(SO.),  =  3Fe,(SO4), ; 

6FeSO,  +  K,CrA  +  7H5SO4  = 

K,S04  +  Cr,(S04)3  +  7H,0  +  (3Fe,(S04),). 

If  in  the  above  case  hydrochloric  acid  is  used  instead 
of  sulphuric,  fourteen  molecules  of  the  former  must  be 
taken  to  supply  the  necessary  hydrogen. 


138       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS, 

The  seven  liberated  atoms  of  oxygen  must  have 
fourteen  atoms  of  hydrogen  to  combine  with. 

Three  of  these  atoms  of  oxygen  liberate  six  uni- 
valent,  or  three  bivalent,  acidulous  radicals. 

Therefore,  since  one  molecule  of  K2CraO7  will  give 
up  for  oxidizing  purposes  three  atoms  of  oxygen, 
which  are  equivalent  chemically  to  six  atoms  of  hydro- 
gen, one  sixth  of  the  molecular  weight  in  grammes  of 
the  dichromate,  dissolved  in  sufficient  water  to  make 
one  litre,  constitutes  a  normal  solution,  and  one  tenth 
of  this  quantity  of  K2Cr2O7  in  a  litre,  a  decinormal 
solution. 

Thus  the  estimation  of  ferrous  salts  is  effected  by 
oxidizing  them  to  ferric  with  an  oxidizing  agent  of 
known  power,  the  strength  of  the  ferrous  salt  being 
determined  by  the  quantity  of  the  oxidizing  agent 
required  to  convert  it  to  ferric. 

Ferri  Carbonas  Saccharatus  (Saccharated  Ferrous 
Carbonate),  FeCO,  =  {  *j  J5.73._*,.l6  (l.I5;3)  gms 

of  saccharated  ferrous  carbonate  are  dissolved  in  10  cc. 
of  diluted  sulphuric  acid  and  the  solution  diluted  with 
water  to  about  100  cc.  The  decinormal  potassium 
dichromate  is  carefully  added,  until  a  drop  of  the  solu- 
tion taken  out  and  brought  in  contact  with  a  drop  of 
freshly  prepared  solution  of  potassium  ferricyanide 
ceases  to  give  a  blue  color. 

The  number  of  cc.  of  the  dichromate  solution  is  read 
off  and  the  following  equations  applied  : 


6FeC08  +  6HaSO,  =  6FeSO4  +  6HaO  +  6COa 

U5-73  I5I-7 

6  6 

694.38  910.2 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       139 

then 

6FeCO3  or  6FeSO4  +  K2Cr2O7  +  ;H2SO4  = 

6)694.38  6)910.2  6)293.78 

10)115.73  10)151.7  10)  48.96 

TI-573  Sms-        *5'17  Sms-  4.896  gms.,  or  looo  cc..?[  K2Cr2O7  V.S. 


K,S04  +  Cr2(S04)3  +  7H20  +  3Fe2(SO4)3. 

N 
Thus  each  cc.  of  —  K2Cr2O7  represents  0.011573  gm. 

of  pure  ferrous  carbonate  or  0.005588  gm.  of  metallic 
iron. 

The  U.  S.  P.  saccharated  ferrous  carbonate  requires 

N 
about  15  cc.  of  —  K2Cr2O7  V.  S.  for  complete  neutral- 

ization, corresponding  to  about  15$. 

.011573  X  15  =0.173585  gm. 
0.173585  X  IPO  = 
I-I573 

If  strong  sulphuric  acid  is  added  to  saccharated  fer- 
rous carbonate  it  will  char  the  sugar,  and  a  black  mass 
of  burnt  sugar  is  obtained.  This  may  be  prevented 
by  adding  water  first  and  then,  slowly,  the  sulphuric 
acid. 

Instead  of  sulphuric  acid,  hydrochloric  acid  may  be 
used.  This  will  not  char  the  sugar  ;  but  the  ferrous 
chloride  which  is  then  formed  is  too  readily  oxidized 
by  the  air. 

It  has  also  been  suggested  that  as  hydrochloric  acid 
so  rapidly  converts  ordinary  sugar  into  invert  sugar 
as  to  render  it  easily  attacked  by  the  dichromate,  it 
should  be  cautiously  used,  if  at  all.  Phosphoric  acid 


140      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

has  none  of  these  disadvantages,  and  may  be  employed 
with  good  results. 

In  making  estimations  of  ferrous  salts  with  potas- 
sium dichromate,  care  should  be  taken  to  avoid  atmos- 
pheric oxidation.  It  is  good  practice  to  calculate 
approximately  how  much  of  the  standard  solution  will 
probably  be  required  to  complete  the  oxidation,  and 
then  add  almost  enough  of  the  standard  solution  at 
once,  instead  of  adding  it  slowly. 

A  white  porcelain  slab  is  then  got  ready,  and  placed 
alongside  of  the  flask  in  which  the  titration  is  to  be 
performed.  Upon  this  slab  is  placed  a  number  of 
drops  of  the  freshly  prepared  solution  of  potassium 
ferricyanide,  and  at  intervals  during  the  titration  a 
drop  is  taken  from  the  flask  on  a  glass  rod  and  brought 
in  contact  with  one  of  the  drops  on  the  slab.  The 
glass  rod  should  always  be  dipped  in  clean  water  after 
having  been  brought  in  contact  with  a  drop  of  the 
indicator. 

When  a  drop  of  the  solution  ceases  to  give  a  blue 
color  on  contact  with  the  indicator,  the  reaction  is 
complete. 

Ferrous  Sulphate,  FeSO4  +  ;H2O  =  j  ^g'42.- 
Dissolve  about  one  gramme  of  crystallized  ferrous  sul- 
phate in  a  little  water,  add  a  good  excess  of  sulphuric 
or  hydrochloric  acid,  titrate  with  the  decinormal  potas- 
sium dichromate  V.  S.  as  directed  under  Ferrous  Car- 
bonate, and  apply  the  following  equation  : 
6(FeSO(.7HaO)  +  K.Cr,O,  +  7H,SO4  = 

6)1668  6)293.78 

10)  278  io)  48.96 

27.8  gms.  4.896  gms.,or  1000  cc.       K2Cr2O,  V.  S. 

3Fe,(SOJ.  +  K.SO.  +  Cr,(SOJ,  +  49H,O. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.        14! 

N 
Thus  each   cc.  of  the  —   K2Cr2O7  V.  S.  represents 

0.0278  gm.  of  crystallized   ferrous  sulphate  or  0.0152 
anhydrous.     If  I  gm.  of  the  salt  is  taken  and  dissolved 
as  above,  it  should  require  about  37  cc.  of  the  standard 
solution,  equivalent  to  about  ioo#. 
Anhydrous  Ferrous  Sulphate.  — 


6FeS04  +  K2CrA  +  / 
6)912  6)293.78 

10)152  10)48.96  N 

15.2  gms.         4.896  gms.,  or  1000  cc.  —  K2Cr2O7  V.  S. 

SFe/SO,),  +  K2SO.  +  Cr,(SO4).  +  ;H2O. 

Each  cc.  of  the  standard  solution  represents  0,0152 
gm.  of  real  ferrous  sulphate  or  ^.0056  gm.  of  metallic 
iron. 

Dried  (Exsiccated)  Ferrous  Sulphate  of  the  U.  S.  P. 
has  the  approximate  composition  FeSO4  -|-  3H2O. 

It  is  tested  in  the  same  manner  as  the  anhydrous 
ferrous  sulphate. 

Granulated  Ferrous  Sulphate,  FeSO4  +  7H,O,  is 
tested  in  the  same  manner  as  crystallized  ferrous  sul- 
phate, with  which  it  should  correspond  in  strength. 

ESTIMATION    OF    FERROUS    SALTS   WITH    POTASSIUM- 
PERMANGANATE  SOLUTION. 

The  action  of  potassium  permanganate  in  oxidation 
is  very  similar  to  that  of  the  dichromate. 

The  molecule  2KMnO4  has  8  atoms  of  oxygen, 
which  it  gives  up  in  the  process  of  oxidation.  These  8 
atoms  of  oxygen  unite  with  the  replaceable  hydrogen 


142       A   TEXT-BOOK   OF  VOLUMETRIC    ANALYSIS. 

of   an    accompanying   acid,    liberating    an    equivalent 
amount  of  acidulous  radical. 

Three  of  these  atoms  of  oxygen  liberate  sufficient 
acidulous  radical  to  combine  with  the  potassium  and 
manganese  of  the  permanganate,  while  the  other  five 
atoms  are  available  either  for  direct  oxidation  or 

2KMn04  +  3H2S04=K2S04  +  2MnSO4  +  3H2O  +  50. 

For  combination  with  the  hydrogen  of  more  acid, 
more  acidulous  radical  being  liberated  to  combine  with 
the  salt  acted  upon, 

2KMnO4+8HaSO4=K2SO4+2MnSO4+8H2O+5(SO4). 

5(SO4)  when  combined  with  ioFeSO4  forms  Fe10 
(SO4)15  or  5Fe2(SO4)3,  ferric  sulphate. 

It  is  thus  seen  that  one  molecule  of  potassium  per- 
manganate 2KMnO4  has  the  power  of  converting  10 
molecules  of  a  ferrous  salt  into  the  ferric  state. 

The  equation  in  full  is 

ioFeSO4  +  2KMnO4  +  8H2SO4  = 

K2S04  +  2MnS04  +  8H20  +  5Fe2(SO4), 

We  have  seen  that  2KMnO4  has  5  atoms  of  oxygen 
available  for  oxidizing  purposes,  and  that  each  of  these 
will  combine  with  2  atoms  of  hydrogen.  2KMnO4  is 
consequently  chemically  equivalent  to  10  atoms  of  re- 
placeable hydrogen,  and  a  normal  solution  of  this  salt 
when  used  as  an  oxidizing  agent  is  one  that  contains  in 
I  litre  one  tenth  of  the  molecular  weight  of  2KMnO4, 
and  a  decinormal  solution  one  which  contains  one 
hundredth  of  the  molecular  weight. 


A    TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.        143 

When  potassium  permanganate  is  brought  in  contact 
with  a  ferrous  salt  or  other  oxidizable  substance,  it  is 
decomposed  and  decolorized. 

When  titrating  with  a  standard  solution  of  this  salt 
it  is  decolorized  so  long  as  an  oxidizable  substance  is 
present ;  as  soon,  however,  as  the  oxidation  is  com- 
pleted the  standard  solution  retains  its  color. 

The  end  of  the  reaction,  therefore,  when  permanga- 
nate is  used,  is  the  appearance  of  a  permanent  faint-red 
color. 

This  is  the  principal  advantage  which  permanganate 
has  over  dichromate. 

When  titrating  with  standard  permanganate  solution 
a  glass  stop-cock  burette  should  be  used,  as  the  solu- 
tion is  slightly  affected  by  the  rubber,  on  Mohr's  bu- 
rette. 

Ferrum  Reductum  is  estimated  for  metallic  iron, 
according  to  the  U.  S.  P.,  in  the  following  manner: 

0.56  (0.559)  Sm'  °f  reduced  iron  is  introduced  into  a 
glass-stoppered  bottle,  50  cc.  of  mercuric  chloride  T.  S. 
are  added,  and  the  bottle  heated  on  a  water-bath  for 
one  hour,  agitating  frequently,  but  keeping  the  bottle 
well  stoppered. 

2HgCl2  +  Fea  =  2FeCl2  +  2Hg. 

Then  allow  it  to  cool,  dilute  the  contents  with  water 
to  loo  cc.,  and  filter.  Take  10  cc.  of  the  filtrate,  add  to 
it  locc.  of  diluted  sulphuric  acid,  introduce  the  mixture 
into  a  glass-stoppered  bottle  (having  a  capacity  of 
about  100  cc.),  and  titrate  the  mixture  with  decinormal 
potassium  permanganate  V.  S.  until  a  permanent  red 
color  is  produced. 


144      A   TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

Each  cc.  of  the  standard  solution  represents  ^0.0056 
gm.  of  metallic  iron,  or  io#. 

ioFeSO4  +  2KMnO4  +  8H2SO4  = 

K3S04  +  2MnS04  +  5Fe2(S04)3  +  8H2O. 

To  confirm  the  assay,  add  a  few  drops  of  alcohol  to 
decolorize  (or  decompose)  the  excess  of  permanga- 
nate, then  add  I  gm.  of  potassium  iodide,  and  digest 
for  half  an  hour  at  a  temperature  of  40°  C.  (104°  F.). 

Fe,(S04)3  +  2KI  =  2FeS04  +  I2  +  K2SO4. 

2)112  2)254 

10)  56  10)127 

5-6  "l2T7 

The  cooled  solution  is  mixed  with  a  few  drops  of 
starch  test  solution,  which  gives  it  a  dark-blue  color, 
because  of  the  formation  of  iodide  of  starch.  Then  add 
carefully,  from  a  burette,  decinormal  sodium  thiosul- 
phate  V.  S.  until  the  blue  color  is  discharged. 

I,  +  2(Na1S10,.5HfO)  =  2NaI  +  Na,S4O.+  ioH2O. 

2)254  2)495-28 

10)127  10)247.64  N 

12.7  gms.          24  76  gms.  or  1000  cc.    —  Na2S2O3  V.  S. 

Thus  each  cc.  of  the  standard  thiosulphate  repre- 
sents 0.0127  gm.  of  iodine,  or  0.0056  gm.  of  metallic 
iron. 

In  both  of  these  estimations  the  quantity  of  standard 
solution  used  should  be  the  same. 

The  U.  S.  P.  requirement  is  8  cc. 

0.0056  X  8  =  0.0448  gm. 
^.0448  X  IPO  _ 
0.056 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS,        145 

Ferrous  Sulphate  (Crystallized),  FeSO4  +  7H2O  = 
>277«42i — *i.39  (1.3871)  gms.  of  ferrous  sulphate  are 

dissolved  in  about  25  cc.  of  water,  and  the  solution 
acidulated  with  sulphuric  acid.  Decinormal  potassium 
permanganate  V.  S.  is  then  delivered  in  from  a  burette 
until  a  permanent  pink  color  is  obtained,  indicating  the 
complete  oxidation  of  the  ferrous  salt. 

io(FeSO4  +  7H20)  +  2KMnO4  +  8H2SO4  = 

100)2774.2  100)315.34  N 

27. 742  gms.  3.1534  gms.  or  1000  cc.   —    stand- 

ard solution. 

5Fe3(SO4)3  +  K2S04  +  2MnSO4  +  8H2O. 

Thus  each  cc.  of  the  standard  solution  represents 
0.027742  gm.  of  crystallized  ferrous  sulphate. 

Not  less  than  50  cc.  should  be  used  before  the  po- 
tassium permanganate  ceases  to  be  decolorized. 

0.027742  X  50   =  i. 387100  gms. 
1.387100  X  ioo  _ 
1.3871 

Granulated  Ferrous  Sulphate,  FeSO4  +  7H2O,  is  esti- 
mated in  the  same  way  as  the  foregoing,  and  should 
correspond  with  it  in  strength. 

Exsiccated  (Dried)  Ferrous  Sulphate. — This  salt  is 
tested  in  the  same  manner  as  the  other  two  sulphates. 
It  contains  a  larger  percentage  of  ferrous  sulphate  than 
the  other  two,  having  less  water  of  crystallization.  Its 
composition  is  approximately  FeSO4  +  3H,O. 

In  estimating  ferrous  sulphate  in  this  salt  the  water 
of  crystallization  is  not  taken  into  account.  Then  by 


146       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

deducting  the  percentage  of  ferrous  sulphate  from  100 
the  percentage  of  water  of  crystallization  is  obtained. 


N 


ioFeSO4  +  2KMnO4  +  8H3SO4 
100)1520          103)315.34 

15.20  gms.  3-1534  gms.  or  1000  cc.  —  standard  solution. 

=  5Fe3(SO4)3  +  K2SO4  +  2MnSO4  +  8H2O. 

Each  cc.  of  the  standard  solution  represents  0.0152 
gm.  of  anhydrous  (real)  ferrous  sulphate.  If  one  gm.  of 
the  dried  salt,  treated  as  above  described,  requires 

N 
48  cc.  of  —  permanganate  solution,  it  contains 

0.0152  X  48  =  0.7296  gm., 

or  72.96$  of  real  ferrous  sulphate,  and  100.00  —  72.96 
=  27.04$  of  water  of  crystallization. 

Any  salt  may  be  analyzed  in  this  way  for  water  of 
crystallization.  If  the  salt  is  ptire,  the  difference  be- 
tween the  percentage  of  real  salt  and  100  always  repre- 
sents the  percentage  of  water  of  crystallization. 

ESTIMATION  OF   HYPOPHOSPHOROUS  ACID,  HYPOPHOS- 
PHITES,   AND   OTHER  OXIDIZABLE   SUBSTANCES. 

Acidum  Hypophosphorosum  Dilutum. — An  aque- 
ous solution  containing  about  10  per  cent,  by  weight, 
of  absolute  hypophosphorous  acid. 

(H3P03)     HPH.O.  = 

N 
This  acid  may  be  tested  by  neutralization  with   — 

potassium  hydrate  V.  S.,  as  described  on  page  79. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       147 

The  U.  S.  P.  also  directs  the  estimation  by  residual 
titration,  given  below. 

0.5  gm.  of  diluted  hypophosphorous  acid  is  mixed 
with  7  cc.  of  sulphuric  acid,  and  35  cc.  of  decinormal 
potassium  permanganate  V.  S.,  and  the  mixture  boiled 
for  fifteen  minutes. 

The  potassium  permanganate,  in  the  presence  of 
sulphuric  acid,  oxidizes  the  hypophosphorous  acid  to 
phosphoric,  as  the  equation  shows  : 


5HPH2O2  +  6H,SO4  -f  2(2KMnO4) 

2)32940  2)630.68 

100)164.7  100)315.34  N 

1.647  gms.  3-1534  gms.  or  1000  cc.  —  V.  S. 

=  5H3P04  +  6H20  +  2K2S04  +  4MnSO4. 

Each  cc.  of  the  decinormal  V.  S.  represents  0.001647 
gm.  of  absolute  hypophosphorous  acid.  The  quantity 
of  permanganate  solution  directed  to  be  added  is 
slightly  in  excess.  The  excess  is  then  ascertained  by 
retitration  with  decinormal  oxalic  acid  V.  S.  Each  cc. 
of  oxalic  acid  required  corresponds  to  one  cc.  of  deci- 
normal permanganate  V.  S.,  which  has  been  added  in 
excess  of  the  quantity  actually  required  for  the  oxida- 
tion. 

The  excess  of  permanganate  colors  the  solution  red, 
and  the  oxalic  acid  V.  S.  is  then  added  until  the  red 
color  just  disappears,  which  indicates  that  the  excess 
of  permanganate  is  decomposed. 

2KMn04  +  5(H2C20,2H20)  +  3H2SO4 

=  K2S04  +  2MnS04  +  i8H20  +  ioCO2. 

If  4.7  cc.  of  decinormal  oxalic  acid  V.  S.  are  required, 
it  indicates  that  35  cc.  —  4.7  cc.  =  30.3  cc.  of  deci- 


148       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

normal  permanganate  were  actually  used  up  in  oxidizing 
the  hypophosphorous  acid. 
Therefore 

0.001647  gm.  X  30.3  =  0.0499  gm., 

or    ?^99_X_^  =  9.98^  of  HPH  A- 

In  the  above  process  the  boiling  facilitates  the  oxida- 
tion, but  if  the  acid  is  boiled  before  it  is  completely 
oxidized  it  will  decompose.  Hence  the  necessity  for 
adding  an  excess  of  the  permanganate  and  retitrating. 

Calcium  Hypophosphite,  Ca(PH2O2),  =  j  *j^*67. 

—  O.I  gm.  of  the  salt  is  dissolved  in  10  cc.  of  water, 
then  10  cc.  of  sulphuric  acid  and  50  cc.  of  decinormal 
potassium  permanganate  V.  S.  are  added,  and  the  mix- 
ture boiled  for  fifteen  minutes. 

The  excess  of  permanganate  is  then  found  by  reti- 
trating with  decinormal  oxalic-acid  solution. 

The  reactions  which  take  place  are  expressed  by  the 
following  equations  : 

5Ca(PHQ02)2  +  5H2S04  =  5CaSO4  +  ioHPH2Oa  ;     (i) 


ioHPH2O5 

=  ioH8PO4  +  i2H2O  +  4K2SO4  +  8MnSO4.     (2) 

These  two  reactions  may  be  written  together  thus  : 
SCa(PH,0,),  +  I7H,SO.  +4(2KMn04) 

4)848.35  4)1261.36 

100)212.08  IOQ)  3I5-34  [ard  V.  S. 

2.1208  gms.  3-1534  gms.  or  1000  cc.  stand- 

=  5CaS04  +  4K,S04  +  8MnSO4  +  ioH3PO4  +I2H2O. 


A  TEXT-BOOK   OP  VOLUMETRIC   ANALYSIS.       149 

Thus  each  cc.  of  the  standard  permanganate  repre- 
sents 0.0021208  gm.  of  pure  Ca(PH2O2)a.  50  cc.  of 
decinormal  potassium  permanganate  are  about  3  cc. 
more  than  is  necessary  to  oxidize  O.I  gm.  of  pure  cal- 
cium hypophosphite.  Therefore  not  more  than  3  cc. 
of  the  standard  oxalic-acid  solution  should  be  required 
to  decolorize  the  solution  to  which  50  cc.  of  perman- 
ganate has  been  added. 

Then 

0.0021208  gm.  x  47  —  .09968  gm. 
0.9968  X  ioo 


O.I 


=  99.68$  pure  salt. 


Ferric  Hypophosphite,    Fe,(PH.OJ.  =   j  ^°\-04. 

—This  salt  is  estimated  in  the  same  manner  as  the  fore- 
going. 

o.i  gm.  is  dissolved  in  10  cc.  of  water,  then  10  cc.  of 
sulphuric  acid  and  50  cc.  of  decinormal  potassium  per- 
manganate V.  S.  are  added,  and  the  mixture  boiled 
for  15  minutes. 

The  quantity  of  permanganate  solution  here  added 
is  slightly  in  excess  of  the  quantity  actually  required 
to  oxidize  the  hypophosphite.  The  excess  is  deter- 
mined by  retitrating  with  decinormal  oxalic  acid  V.  S., 
which  corresponds  volume  for  volume  with  the  per- 
manganate. 

Not  more  than  3  cc.  of  the  standard  oxalic  acid  so- 
lution should  be  required  to  decolorize  the  excess  of 
permanganate,  which  means  that  47  c.c.  of  the  per- 


150      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

manganate  should  actually  be  required  to  oxidize  the 
O.I  gm.  of  hypophosphite  taken. 

The  reaction  is  illustrated  by  the  following  equation : 

SFe/PH  A),+5 1  H,SO.+  i2(2KMn04) 

12)2505.20  12)3784.08 

ioo)~gc8.77  IPO)  315.34  N  v  s 

2.0877  gm.  3.i534gms.or  looocc.io 

=5FeJ(SO)),+K1SO.+24MnSO<+3oHJPO.+36HA 

N 

This  ?hows  that  each  cc.  of  —  potassium  permanga- 
nate V.  S.  represents  0.0020877  gm.  of  ferric  hypophos- 
phite. If  47  cc.  are  required  to  oxidize  O.I  gm.  of  the 
salt,  the  latter  contains  0.0020877  X  47  —  0.0981+  gm., 
or  98.1+  %  of  pure  salt. 

Potassium  Hypophosphite,  KPH,O2  =  j  *j°3"91. 

—o.i  gm.  of  dry  potassium  hypophosphite  is  dissolved 
in  about  to  cc.  of  water,  then  7.5  cc.  of  sulphuric  acid 
and  40  cc.  of  decinormal  potassium  permanganate  V.  S. 
are  added,  and  the  mixture  is  boiled  for  15  minutes. 

Decinormal  oxalic  acid  is  then  carefully  delivered 
into  the  mixture  until  the  red  color,  due  to  the  excess 
of  permanganate,  is  discharged.  The  number  of  cc.  of 
the  standard  oxalic  acid  required  for  this  purpose,  sub- 
tracted from  the  40  cc.  of  permanganate  originally 
added,  gives  the  quantity  of  permanganate  which  was 
actually  required  for  the  oxidation  of  the  hypophos- 
phite. If  the  salt  conforms  in  purity  to  the  U.  S.  P. 
requirement,  not  more  than  2  cc.  of  the  oxalic  acid 
V.  S.  will  be  required. 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       !$! 

The  following  equation  illustrates  the  reaction  which 
takes  place  in  this  operation  : 

5KPH2Oa  +  6HaS04  +  2(2KMn04) 

2)519-55  2)630.68 

100)259.77  100)315.34 

2.5977  gm.  3.i534gms. 

or  looo  cc.  —  permaganate  V.  S. 

=  5KH2PO4  +  2KaSO4  +  4MnSO4  +  6H2O. 

Each  cc.  of  decinormal  permanganate  V.  S.  required 
for  the  oxidation  of  the  hypophosphite,  represents 
0.0025977  gm.  of  the  pure  salt.  If  38  cc.  are  required, 
then  0.0025977  X  38  =  .0987126  gm.,  or  98.7+  %. 

Sodium      Hypophosphite,      NaPH2Os  +  H2O  = 

\  #     i"     . — o.i  gm.  of  the  dry  salt  is  dissolved  in  10 

cc.  of  water  and  mixed  with  7.5  cc.  sulphuric  acid  and 
40  cc.  of  decinormal  potassium  permanganate  V.  S. 
The  mixture  is  then  boiled  for  15  minutes,  and  titrated 
with  decinormal  oxalic-acid  solution  to  determine  the 
excess  of  permanganate. 

Not  more  than  3  cc.  of  the  oxalic  acid  V.  S. 
should  be  required  to  discharge  the  red  color,  which 
means  that  O.I  gm.  of  the  salt  should  require  37  cc.  of 

N 
-  permaganate  solution  for  its  oxidation. 

The  following  equation  shows  the  reaction : 

5(NaPH202.H2O)  +  6H2SO4  +  2(2KMnO4)  = 

2)529.2  2)630.68 

100)264.6  100)315.34 

2.646  gm.  3.1534  gm.,      N 

or  1000  cc.  —  V.S. 

5NaH2P04  +  2NaaS04  +  4MnSO4  +  1 1  H2O. 


152       A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

Thus  each  cc.  of  the  decinormal  permanganate  repre- 
sents 0.002646  gm.  of  NaPH2O2. 

Therefore  0.002646  X  37  =  0.097902  gm.  or  97.9$. 

Aqua  Hydrogenii  Dioxidi  U.  S.  P.  (Solution  of 
Hydrogen  Peroxide). — It  is  described  in  the  U.  S.  P. 
as  an  aqueous  solution  of  hydrogen  dioxide,  H2O2  = 

•j  *          ,  slightly  acid   and    containing   about  3$,   by 

weight,  of  pure  dioxide,  corresponding  to  10  volumes 
of  available  oxygen. 

This  substance  is  official  for  the  first  time  in  the 
'U.S.  P.  1890,  in  which  methods  for  its  preparation, 
preservation,  and  assay  are  given.  Solution  of  hydro- 
gen peroxide  is  an  important  commercial  product, 
being  used  in  the  arts  as  well  as  in  medicine. 

It  is  sold  as  containing  5,  10,  15,  or  20  volumes  of 
oxygen,  in  solution.  This  should  mean  that  a  given 
volume  of  the  solution  yields  from  itself  5,  10,  15,  or  20 
times  its  own  volume  of  oxygen. 

Thus,  I  cc.  of  a  5-volume  solution  yields  5  cc.  of 
oxygen ;  a  lo-volume  solution  is  one  of  which  I  cc. 
will  yield  10  cc.  of  oxygen  ;  etc. 

Many  solutions  of  hydrogen  dioxide  are  sent  into 
the  market  under  false  pretences,  being  labelled  as  con- 
taining 10,  15,  or  20  volumes  of  oxygen. 

It  is  true  a  given  volume  of  these  solutions  will 
yield  the  specified  volume  of  oxygen  when  decom- 
posed with  potassium  permanganate,  but  half  of  this 
oxygen  comes  from  the  permanganate  itself.  There- 
fore the  peroxide  of  hydrogen  solution  contains  only 
half  as  much  available  oxygen  as  is  given  off  in  this 
decomposition. 

Freshly  bought  samples  of  the  five  largest  manufac- 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       I $3 

turers,  according  to  the  analyses  of  Dr.  Edward  R. 
Squibb  (Ephemeris,  vol.  IV.  No.  2),  gave  9.2,  8.7,  8.4, 
10.9.  9.7,  8.6,  8.5,  7.3,  and  7.4  volumes.  All  of  these 
were  labelled  as  being  of  15  volumes  strength.  The 
author  has  had  a  similar  experience. 

In  its  purest  and  most  concentrated  form  peroxide 
of  hydrogen  is  a  syrupy  colorless  liquid,  having  an  odor 
resembling  that  of  chlorine  or  ozone. 

One  cc.  of  this  concentrated  hydrogen  peroxide  when 
decomposed  at  o°  C.  evolves  330.3  times  its  own  volume 
of  oxygen,  at  a  pressure  of  760  mm.  at  45°  N.  latitude. 

At  a  temperature  of  100°  C.  (212°  F.)  H2Oa  decom- 
poses rapidly  into  water  and  oxygen.  This  change 
also  takes  place  at  ordinary  temperatures,  but  more 
slowly.  In  diluted  solutions  it  is  more  stable,  and  may 
be  concentrated  by  boiling  without  suffering  much  de- 
composition. 

Dr.  Squibb  made  a  series  of  experiments  in  order  to 
prove  this,  as  well  as  the  fact  that  solutions  of  hydro- 
gen peroxide  when  kept  in  open  vessels  at  the  ordi- 
nary temperature  become  stronger,  instead  of  weaker 
as  was  generally  supposed.  The  water  evaporates 
more  rapidly  than  the  peroxide  decomposes.  Part  of 
the  results  of  these  experiments  as  published  in  the 
Ephemeris,  vol.  IV.  No.  2,  is  as  follows : 

A  freshly  made  solution  that  yielded  10.3  volumes 
of  available  oxygen  was  taken  as  the  basis  of  the  ex- 
periment. The  evaporation  was  done  on  a  water-bath, 
at  temperatures  varying  from  55°  to  62°  C.  (131°  to 
143.6°  F.) ;  one  cc.  of  the  concentrated  solution  being 
taken  out  for  testing  after  each  evaporation. 
200  cc.  evaporated  in  2  hours  to  100  cc.  tested  20.6 
volumes  :  no  apparent  loss. 


154      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

100  cc.  of  the   io.3-volume  solution   were  added,  and 

evaporated  in  2  hours  to  100  cc.,  tested  29.6 

volumes:   1.3  volumes  loss. 
IOO  cc.  of  the   io.3-volume  solution   were  added,  and 

evaporated  in  2  hours  to  100  cc.,  tested  36.5 

volumes:  4.7  volumes  loss. 
IOO  cc.  of  the   io.3-volume  solution  were  added,  and 

evaporated  in  2.5  hours  to  23  cc.,  tested  146.8 

volumes. 

Another  series  of  evaporations  were  made  at  higher 
temperatures,  which  also  showed  an  increase  in  strength, 
but  the  loss  was  a  little  larger. 
The     Assay     of     Hydrogen     Peroxide,     H2O2 

=  j*33'92.—  The    U.    S.    P.    method    is   as   follows: 
'     34 

10  cc.  of  the  solution  are  diluted  with  water  to  make 
IOO  cc.  Transfer  17  cc.  of  this  liquid  (containing 
1.7  cc.  of  the  solution  of  HaO3)  to  a  beaker,  add  5  cc. 

N 
of  diluted  sulphuric  acid,  and  then  from  a  burette  — 

potassium  permanganate  V.  S.  until  the  liquid  just 
retains  a  faint-pink  tint  after  being  stirred. 

The  reaction  is  expressed  by  the  following  equation  : 


5H202 
100)169.6  100)315.34  N 

1.696^015.  3.1534  gms.  or  1000  cc.  -    permanganate  V.  S. 

*ioo)i70. 

1.70 

=  K2SO4  +  2MnS04  +  8H20  +  sO2. 

N 
Thus  each  cc.  of   the  —  potassium    permanganate 

represents  .001696  (^.0017)  gm.  of  absolute  hydrogen 
dioxide. 


A  TEXT-BOOK   OK  VOLUMETRIC   ANALYSIS.       -155 

The  U.  S.  P.  requires  that   1.7   cc.  of  the  solution  of 

N 
peroxide  should  decolorize  30  cc.  of  —  permanganate 

solution.  • 

This  corresponds  to  3  per  cent,  by  weight,  of  H2O2. 

.0017  X  30  =  .051  gm. 
.051  X  100 


Estimation  of  Volume  Strength.  —  Let  us  look  at 
the  above  equation  in  a  different  light. 

We  there  see  that  when  potassium  permanganate 
and  hydrogen  peroxide  react,  10  atoms  of  oxygen  are 
liberated. 

The  permanganate  itself  when  decomposed  liberates 
five  atoms  of  oxygen.  Therefore  of  the  above  ten 
atoms  only  five  come  from  the  peroxide  of  hydrogen. 


2KMn04+sH1S(54  =  K2SO4  +  2MnSO4  +  3H2O  +  50. 


In  order  to  find  the  factor  for  volume  of  available 
oxygen,  see  the  following  equation,  etc.: 


100)315.34  N 

3.i534gms.  or  1000  cc.  of  ~  V.  S. 

=  K2SO4  +  2MnSO4  +  8H2O  +  SO  +  5O. 

100)79.8 

.798  gm. 
100)  80 

*.8o  gm. 


156      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

N 

Thus  it  is  seen  that   each  cc.  of     -  potassium  per- 
manganate represents  .000798  (*.ooo8)  gm.  of  oxygen. 
But  we  wish  to  find  the  volume  of  oxygen,  not  the 

N 
weight   represented  by  I   cc.  of  the  —  permanganate. 

1000  cc.   of   oxygen   at  o°  C.   and   760  mm.  pressure 
weigh  1.424488  grammes,  *(i.43  gms.). 

Therefore,  if  1.43  gms.  measure  1000  cc.,  .0008  gm. 
will  measure  x. 


looo  X  .0008 

— —        -  0.5594  cc. 

The  factor,  then,  for  volume  of   oxygen,  liberated 

N 

when  peroxide  of  hydrogen  is  titrated  with  —  potas- 
sium permanganate   is  0.5594,  and  the  number  of  cc. 

N 
of  the  —   potassium   permanganate  consumed   in  the 

titration  gives  the  volume  of  oxygen  liberated  by  the 
quantity  of  hydrogen  peroxide  taken. 

N 
Thus  if  30  cc.  of  the  —  V.  S.  were  required, 

0.5594  X  30  =  16.782  cc.  of  oxygen, 
1.7)16.782 

9.87  volume  strength. 

or  the  number  of  cc.  of  oxygen  liberated  by  I  cc.  of 
the  peroxide  solution  tested. 

It    is   convenient   to   operate   upon    I    cc.   hydrogen- 
peroxide  solution.     Then  each    cc.    of  potassium  per- 


A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.       157 

manganate  V.  S.  used  will  represent  0.5594  cc.  of  avail- 
able oxygen,  or  0.0008  gm'.  of  oxygen,  and  it  is  only 
necessary  to  multiply  the  cc.  by  these  numbers  to 
obtain  the  volume  or  weight  of  available  oxygen. 

Hydrogen-peroxide  solution  may  also  be  volumetri- 
cally  assayed  by  Kingzett's  method,  which  is  described 
in  the  chapter  on  lodimetry. 

The  gasometric  estimation  is  also  described  further 
on. 

Barium    Dioxide     (Barium     Peroxide),     BaO2    = 

I  *tf68*     ' — This  substance   is   assayed  by  treating  it 

with  an  acid,  and  then  estimating  the  liberated  hydro- 
gen dioxide,  as  follows : 

Weigh  off  2.11  gms.  of  the  coarse  powder,  put  it  in 
a  porcelain  capsule,  add  about  10  cc.  of  ice-cold  water, 
then  7.5  cc.  of  phosphoric  acid,  U.  S.  P.,  and  sufficient 
ice-cold  water  to  make  25  cc.  Stir  and  break  up  the 
particles  with  the  end  of  the  stirrer  until  a  clear  or 
nearly  clear  solution  is  obtained,  and  all  that  is  soluble 
is  dissolved. 

5  cc.  of  this  solution  (which  corresponds  to  0.422  gm. 
of  barium  dioxide)  is  measured  off  for  assay. 

Drop  into  this  from  a  burette,  with  constant  stirring, 
decinormal  potassium  permanganate  V.  S.  until  a  final 
drop  gives  the  solution  a  permanent  pink  tint. 

Not  less  than  40  cc.  of  the  decinormal  permanganate 
V.  S.  should  be  required  to  produce  this  result. 

In  this  process,  the  first  step  is  the  formation  of  hy- 
drogen peroxide  by  treating  the  barium  peroxide  with 
phosphoric  acid,  as  illustrated  by  the  following  equa- 
tion : 

BaOa+  H8P04  =  BaHP04  +  HaOa- 


158       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

The  hydrogen  peroxide  is  then  estimated  with  deci- 
normal  permanganate  V.  S. 

5H202  +   2KMn04  +  3H2S04 
100)169.6          100)315.34 

1.696  gms.          3.1534  gms.  or  1000  cc.  5  permanganate  V.  S. 
100)1.70  10 

=  K2SO4  +  2MnSO4  +8H2O  +  sO2. 

N 
Thus  each  cc.  of   -  -  potassium   permanganate  V.  S. 

represents  0.001696  gm.   (^0.0017  gm.)  of  H2O2 ;  and 
since  169.6  gms.  of  H2O2  are  equivalent  to  844.1  gms. 

of  BaO2,  (844.iagms.~i69.6  gin's.)'  l   cc-  of  the  —   perman- 

ganate  solution  corresponds  to  0.008441  gm.  of  BaO2. 

Not   less   than    40  cc.   of    the    decinormal   solution 
should  be  required. 

Thus  .008441  X  40  =  0.3376  gm. 

.3376  X  ioo 


.422 


=  Sofo  of  pure  BaO2. 


Oxalic  Acid,  H2C2O4  +  2H2O  =  j  *\2^7 .  —  Oxalic 

acid  may  be  estimated  either  by  neutralization  with  an 
alkaline  V.  S.,  or  by  oxidation  with  potassium  perman- 
ganate V.  S. 

The  permanganate  is  generally  used  when  the  acid 
is  in  combination  as  oxalate. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       159 
The  reaction  is  illustrated  as  follows  : 

5(H.CA  +  2H,0)  +  3H,SO«  +  2KMnO. 

IOOJ628.5 


6.285  gms.  3.1534  gms.  or  1000 

cc.  —  permanganate  V,  S. 
10 


=  KaSO4  +  2MnSO4  +  i8HaO  +  loCO,. 

N 
Thus  each  cc.   of  the   -  -   permanganate   represents 

0.006285  gm.  of  pure  oxalic  acid  (crystallized). 

Note.  —  It  must  be  remembered,  in  titrating  with  per- 
manganate, that  an  excess  of  sulphuric  acid  is  always 
necessary,  in  order  to  keep  the  resulting  manganous 
compound  in  solution,  by  forming  a  soluble  manganous 
sulphate. 

If  hydrochloric  acid  is  used  the  solution  must  be  very 
dilute,  and  the  temperature  not  raised  too  high,  other- 
wise chlorine  will  be  liberated,  which  will  spoil  the 
analysis. 

It  should  be  borne  in  mind  that  the  solution  of 
potassium  permanganate  should  not  be  filtered  through 
paper,  as  it  is  decomposed  by  organic  matter.  It  may, 
however,  be  filtered  through  gun-cotton  or  glass-wool. 
It  should  never  be  used  in  a  Mohr's  burette. 


l6o       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


TABLE  OF  SUBSTANCES  WHICH  MAY  BE  ESTIMATED  BY  OXIDATION, 
BY  POTASSIUM  BICHROMATE  OR  POTASSIUM  PERMANGANATE, 
SHOWING  FORMULA,  MOLECULAR  WEIGHT,  FACTOR,  ETC. 


Name  of  Substance. 

Formula. 

Mole- 
cular 
Wt. 

Sv.s. 

10 

Used. 

Factor 

(exact). 

Ac.  hypophosphorous  

HPH2O2 

65.88 

aKMnO.* 

Ac   oxalic  (crystallized) 

2KMnO4 

Barium  dioxide     

BaOj 

168.82 

2KMnO4 

008441 

Calcium  hypophosphite  

Ca(PH2O2)Q 
Fe2(PH2O2)6 

169.67 

2KMn04* 
2KMnO4* 

.0021209 

Ferrous  carbonate 

FeCO3 

1  2K.IVfnO4    f 

Ferrous  oxide        .        .  .        .... 

FeO 

71.84 

J   K2Cr2O-r   1 

j  2KMnO4   I 

Ferrous  sulphate  (anhydrous)  

FeSO4 

151-58 

S   K2Cr207   J 
1   2KMnO4  | 

-015170 

Ferrous  sulphate  (dried)  

2FeS04-HH20 

357-28 

«  K2Cr207  J 
1   2KMnO4   f 

.017864 

Ferrous  sulphate  (crystallized).  .  . 

FeS04  +  7H20 

277.42 

j  K2Cr207   I 
)  2KMn04   f 

.027742 

Ferrum  (metallic)  

Fe2 

111.76 

j   K2Cr207   | 

.005588 

1  2KMnO4    \ 

Hydrogen  dioxide  
Oxygen,wt.  of  available,  in  H2O2 

H£< 

33-Q2 

2KMnO4 
2KMn04 

.001696 
.000798 

'*        volume 
Potassium  hypophosphite  

KPH^Oo 

103.91 

2KMnO4 
2KMnO4* 

•5S94 
.002598 

Sodium  hypophosphite  

NaPH2O2-i-H2O 

105.84 

2KMnO4* 

.002646 

*  Determined  by  residual  titration  with  decinormal  oxalic  acid  V.  S. 
The  factors  given  in  this  table  are  calculated  upon  the  revised  atomic  weights, 
which  are  indorsed  by  the  U.  S.  P. 


A  TEXT  BOOK   OF  VOLUMETRIC   ANALYSIS.       l6l 


CHAPTER    XII. 
ANALYSIS  BY  INDIRECT  OXIDATION. 

THIS  method  of  analysis  is  based  upon  the  oxidizing 
power  of  iodine. 

Iodine  acts  upon  the  elements  of  water,  forming 
hydriodic  acid  with  the  hydrogen,  and  liberating  oxy- 
gen in  a  nascent  state. 

Nascent  oxygen  is  a  very  active  agent,  and  readily 
combines  with  and  oxidizes  many  substances,  such  as 
arsenous  oxide,  sulphurous  acid,  sulphites,  thiosul- 
phates,  etc. 

As.0,  +  2H,0  +  21,  -  4HI  +  AsA; 
H2S03  +  H20  +  I,  =  2HI  +  H3S04. 

Therefore  iodine  is  said  to  be  an  indirect  oxidizer, 
and  may  be  used  for  the  estimation  of  a  great  variety 
of  substances,  with  extreme  accuracy. 

The  end  of  the  reaction  in  an  analysis  by  this  method 
is  ascertained  by  the  use  of  starch  test  solution,  which 
produces,  with  the  slightest  trace  of  free  iodine,  a  dis- 
tinct blue  color. 

In  making  an  analysis  with  standard  iodine  solution, 
the  substance  under  examination  is  brought  into  dilute 
solution,  the  starch  solution  added,  and  then  the  iodine, 
in  the  form  of  a  decinormal  solution,  is  delivered  in  from 
a  burette,  stirring  or  shaking  constantly,  until  a  final 


1 62       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

drop  colors  the  solution  blue — a  sign  that  a  slight  ex- 
cess of  iodine  has  been  added. 

Decinortnal  Iodine  V.  S.,  I  =  {  ,|*|»  .J^-gS  J 

in  i  litre. — 12.653  gms.  of  pure  iodine  are  dissolved  in 
300  cc.  of  distilled  water  containing  18  gms.  of  pure 
potassium  iodide.  Then  enough  water  is  added  to 
make  the  solution  measure,  at  15°  C.  (59°  F.),  exactly 
1000  cc.  The  solution  should  be  kept  in  small 
glass-stoppered  vials,  in  a  dark  place. 

The  potassium  iodide  used  in  this  solution  acts 
merely  as  a  solvent  for  the  iodine. 

If  pure  iodine  be  not  at  hand,  it  may  be  prepared 
from  the  commercial  article  as  follows : 

Powder  the  iodine  and  heat  it  in  a  porcelain  dish 
placed  over  a  water-bath,  stirring  constantly  with  a 
glass  rod  for  20  minutes.  Any  adhering  moisture,  to- 
gether with  any  cyanogen  iodide,  and  most  of  the 
iodine  bromide  and  iodine  chloride,  is  thus  vaporized. 

Then  triturate  the  iodine  with  about  5  per  cent,  of 
its  weight  of  pure,  dry  potassium  iodide.  The  iodine 
bromide  and  chloride  are  thereby  decomposed,  potas- 
sium bromide  and  chloride  being  formed,  and  iodine 
liberated  from  the  potassium  iodide. 

The  mixture  is  then  returned  to  the  porcelain  dish, 
covered  with  a  clean  glass  funnel,  and  heated  on  a  sand- 
bath.  A  pure  resublimed  iodine  is  then  obtained. 

If  pure  iodine  is.  used  in  making  this  solution,  there 
is  no  necessity  for  checking  (standardizing)  it. 

But  if  desired,  the  solution  may  be  checked  against 
pure  arsenous  acid  or  pure  sodium  thiosulphate. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       163 
ESTIMATION   OF  ARSENOUS   ACID. 

Arsenous  Anhydride,  Arsenic  Trioxide,  As2O,  = 
I  #r9g  • — When  arsenous  acid  is  brought  in  contact 

with  iodine  in  the  presence  of  water  and  an  alkali,  it  is 
oxidized  into  arsenic  acid,  and  the  iodine  is  decolorized. 
The  reaction  is: 

As,03  +  2l2  +  2H20  =  As2OB  +  4HI ; 

NaHC03  +  HI  =  Nal  +  H2O  +  CO2. 

The  alkali  should  be  in  sufficient  quantity  to  combine 
with  the  hydriodic  acid  formed,  and  must  be  in  the 
form  of  potassium  or  sodium  bicarbonate. 

The  hydroxides  or  carbonates  should  not  be  used,  as 
they  interfere  with  the  indicator.  Starch  solution  is 
used  as  the  indicator,  a  blue  color  being  formed  as  soon 
as  the  arsenous  acid  is  entirely  oxidized  into  arsenic 
acid. 

o.i  gm.  of  arsenous  acid  is  accurately  weighed  and 
dissolved,  together  with  about  I  gm.  of  sodium  bicar- 
bonate, in  20  cc.  of  water  heated  to  boiling.  Allow  the 
liquid  to  cool,  add  a  few  drops  of  starch  T.  S.,  and  allow 
the  decinormal  iodine  V.  S.  to  flow  in,  shaking  or  stir- 
ring the  mixture  constantly,  until  a  permanent  blue 
color  is  produced.  The  following  equation  illustrates 
the  reaction  : 

As,03   +    5H20  +  2l2  =  4HI  +  2H3As04. 

4)197.68  4)506 

10)  49-42  10)126.5  N 

4.942  gms.  12.65  gms.  or  1000  cc.  —  Iodine  V.  S, 


164      A   TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

N 

Thus  it  is  seen  that  each  cc.  of  the  —  standard  so- 

10 

lution  represents  0.004942  gm.  of  pure  As2O,. 
If  20  cc.  are  consumed,  then 

0.004942  X  20  =  0.09884  gm. 
.09884  X  ioo 

— —      ~  =  9 


The  U.  S.  P.  requirement  is  98.8$  of  As3O3.  The 
starch  T.  S.  is  not  used  in  the  U.  S.  P.  process,  and  the 
end  of  the  reaction  is  known  by  the  iodine  being  no 
longer  decolorized.  But  with  starch  the  indication  is 
exceedingly  delicate,  and  it  should  always  be  used. 

Liquor  Acidi  Arsenosi,  U.  S.  P. — Measure  accu- 
rately 10  cc.  of  the  solution,  add  to  it  I  gm.  of  sodium 
bicarbonate,  and  boil  for  a  few  minutes.  Then  allow 
the  liquid  to  cool,  and  dilute  it  to  50  cc.  with  water. 
A  little  starch  T.  S.  is  then  added  and  the  decinormal 
iodine  V.  S.  run  in  from  a  burette,  until  a  final  drop 
produces  the  blue  color  of  starch  iodide. 

N 
Each  cc.  of  —  I.  V.  S.  represents  0.004942  gm.  of 

As2O3.     (See  Estimation  of  Arsenous  Acid.) 

The  U.  S.  P.  requirement  is  that  24.7  cc.  of  the 
liquor  acidi  arsenosi,  when  treated  as  above,  will  con- 
sume 49.4  to  50  cc.  of  decinormal  iodine  V.  S.  Use 
2  gms.  of  the  bicarbonate. 

0.004942  X  50  —  0.2471  gm. 

0.2471  X  ioo 

=.  \% 

24.7 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       165 


Liquor  Potassii  Arsenitis,  U.  S.  P.  (Fowler's  Solu- 
tion).— The  process  is  exactly  the  same  as  the  fore- 
going. 24.7  cc.,  diluted  and  treated  with  2  gms.  of 
sodium  bicarbonate,  should  require  49.4  to  50  cc.  of 

N 
the  —  I.  V.  S.,  corresponding  to  \<f>  of  As2O3. 

Sulphurous  Acid  (Acidum  Sulphurosum,  U.  S.  P.) — 
This  is  an  aqueous  solution  of  sulphur  dioxide,  SO2  = 

*^'^,  containing  6.4  per  cent.,  by  weight,  of  the  gas. 

Sulphurous  acid  when  brought  in  contact  with  iodine 
is  oxidized  into  sulphuric,  the  iodine  being  decolorized 
because  of  its  union  with  the  hydrogen  of  the  accom- 
panying water,  forming  hydriodic  acid. 

Two  gms.  of  sulphurous  acid  are  taken  and  diluted 
with  distilled  water  (recently  boiled  and  cooled)  to 
about  25  cc.  The  decinormal  iodine  V.  S.  is  then 
delivered  into  the  solution  (to  which  a  little  starch 
T.  S.  had  been  previously  added)  until  a  permanent 
blue  color  is  produced.  At  least  40  cc.  of  the  standard 
iodine  solution  should  be  consumed  before  this  color 
appears. 

The  following  equations,  etc.,  show  the  reaction  that 
takes  place : 

H2S03  +  H,0  +     I,      =  2HI  +  H9SO4. 

2)8 i. S6  2)253 

10)40.93  10)126.5 

4.093  gms.  12.65  Sms'  or  1000  cc.  —  V.  S. 

N 
Thus  each  cc.  of  the  —  V.  S.  represents  .004093  gm. 

of  pure  H2SO3. 

Sulphurous  acid  being,  however,  looked  upon  as  a 


l66      A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

solution  of  SO2  in  water,  the  quantity  of  this  gas  is 
generally  estimated  in  analysis. 

H20,S02  +  HaO  +      I2      =  2HI  +  H2S04. 

2)63.9  2)253 

10)31.95  10)126.5 

3  195  gms.  12.65  gms. 

N 

Thus  each  cc.  of  -  -  V.  S.  consumed  before  the  blue 
10 

color  appears  represents  0.003195  gm.  of  SO2. 

If  40  cc.  are  consumed   in  the  above  analysis,  the 
2  gms.  contain 

0.003195  X  40  =  0.1278; 
then 

0.1278  X  ioo 

; =  6.39^  Of  S0a. 


The  sulphurous  acid  should  be  diluted  with  distilled 
water  to  below  0.04  per  cent  before  titrating  it ;  for  if 
it  is  not  sufficiently  diluted  there  is  a  risk  of  the  sul- 
phuric acid  formed,  being  again  reduced  to  sulphurous, 
with  liberation  of  iodine,  thus  causing  irregular  results. 

This  may,  however,  be  obviated  by  adding  at  once 

N 
a  measured  excess  of  —  iodine  V.  S.  and  titrating  back 

N 
with  —  sodium  thiosulphate  V.  S. 

The  direction  to  boil  the  distilled  water  is  given  for 
the  purpose  of  freeing  it  from  air,  which  would  have  a 
tendency  to  partially  oxidize  the  sulphurous  acid. 

Sodium  Sulphite,  Na2SO3  +  7H3O  =  j  ^ sS.- 
One  gm.  of  the  salt  is  dissolved  in  25  cc.  of  distilled 


A   TEXT-BOOK   OF    VOLUMETRIC   ANALYSIS.       167 

water  recently  boiled  to  expel  air,  a  little  starch  T.  S. 
is  added,  and  then  the  decinormal  iodine  V.  S.  de- 
livered in  from  a  burette,  until  the  blue  color  of  starch 
iodide  appears,  which  does  not  disappear  upon  shaking 
or  stirring. 

The  reaction  is  expressed  as  follows  : 

NaaSO3  +  ;H2O  +      Ia      =  2NaI  +  HaSO4  +  6HaO. 

2)251.58  2)253 


10)125.79  io)i26.5_  N  ' 

12.579  gms«  12.65  gms-  °r  1000  cc.    -  iodine  V.  S. 


Thus  each  cc.  of  the  standard  solution  represents 
.012579  gm.  of  crystallized  sodium  sulphite. 

If  i  gm.  of  the  salt  is  taken,  to  find  the  percentage 
multiply  the  factor  by  the  number  of  cc.  of  standard 
solution  consumed,  and  the  result  by  100. 

The  U.  S.  P.  requirement  is  96  per  cent.  0.63  gm. 
of  salt  should  require  for  complete  oxidation  48  cc.  of 
the  standard  solution.  Therefore 

.012579  X  48  =  .603792  gm. 
0.603792  X  100 


0.63 


=  95.8^ 


Potassium    Sulphite,     KaSO3  +  2H,O  =  ^194.- 
Operate    upon   0.5   gm.  in  the   same    manner   as   for 
sodium  sulphite. 

KSO,  +  2H30  +      I2      =  2KI  +  HaS04  +  H20. 


2)194  2)253 


10)  97  10)126.5 

9.7  gms.  12.65  gms.  or  1000  cc.  of  standard  V  S. 


l68      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

Each  cc.  of  the  decinormal  iodine  V.  S.  used  rep- 
resents 0.0097  gm.  of  crystallized  potassium  sulphite. 
If  46  cc.  are  used,  the  salt  is  over  89$  strength. 

Sodium  Bisulphite,  NaHSO3  =  j  x1^'*6.— Dis- 
solve 0.26  gm.  of  the  salt  in  20  cc.  of  distilled  water 
which  has  been  previously  boiled  to  expel  air,  add  a 
little  starch  T.  S.,  and  pass  in  the  decinormal  iodine 
V.  S.  from  a  burette,  until  a  permanent  blue  color 
appears.  At  least  45  cc.  should  be  required. 

Apply  the  following  equation  : 

NaHS03  +       I,      +  H,0  =  Nal  +  HI  +  H2SO4. 
2)103.86  2)253 

10)  5I.Q3  10)126.5  N 

5.193  gms.         12.65  gms.  or  1000  cc.  —  V.  S. 

Thus  each  cc.  of  decinormal  iodine  V.  S.  represents 
0.005193  gm.  of  sodium  bisulphite. 

0.005193  X  45  =  0.23368  gm. 
0.23368  X  ioo 


0.26 

Sodium     Thiosulphate     (Sodium     Hyposulphite), 
Na2S203+5H20  -  |  ^47-<H_This  salt>  when  brought 

in  contact  with  iodine,  is  converted  into  tetrathionate 
of  sodium,  and  the  iodine  is  decolorized. 

It  is  estimated  as  follows  :   0.25  gm.  of  the  salt  is 
dissolved  in  10  cc.  of  water,  a  few  drops  of  starch  T.  S. 

N  . 
are  added,  and  then  the  —  iodine  V.  S.  is  delivered  in 

from   a   burette,  until   the   appearance    of   blue  starch 
iodide  indicates  an  excess  of  iodine. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       169 

At  least  9.9  cc.  of  the  standard  solution  should  be 
added  before  a  final  drop  produces  a  permanent  blue 
color. 

The  reaction  is  expressed  as  follows  : 

2(Na,S,0..5H,0)  +      I, 

2)495-28  2)253 

10)247.64  10)126.5  N 

24.764  gms.  12.65  gms-  or  I0°o  cc-  —  L  V.  S. 

=  2NaI  +  Na,S4O6  +  ioH2O. 

Thus  each  cc.  represents  .024764  gin.  of  crystallized 
thiosulphate. 

9.9  cc.  contain  0.024764  gm.  X  9-9  =  .2451636  gm. 
0.2451636  X  ioo 


0.25 


=  98.1; 


Iodine  may  also  be  used  for  estimating  antimonous 
compounds.  The  reaction  is  similar  to  that  with 
arsenous  compounds  ;  thus 

Sb20,  +  2HaO  +  2l3  =  Sb,05  +  4HI. 

Antimony  and  Potassium  Tartrate  (Tartar  Emet- 
ic), 2(K(SbO)C4H408)  +  H20  =  j46442.-This  is 

the  only  antimonial  salt,  a  process  for  the  volumetric 
estimation  of  which  is  given  in  the  U.  S.  P. 

The  U.  S.  P.  directs  that  0331  gm.  of  the  crystal- 
lized salt  or  0.322  gm.  of  the  salt  dried  at  110°  C. 
(230°  F.)  be  taken  for  analysis.  The  salt  is  dissolved 
in  10  cc.  of  water,  and  about  20  cc.  of  a  cold  saturated 
solution  of  sodium  bicarbonate  and  a  little  starch  T.  S. 
added.  The  decinormal  iodine  V.  S.  is  then  delivered 
in  from  a  burette,  until  the  blue  color  of  the  starch 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

iodide  makes  its  appearance,  indicating  that  the  salt 
has  been  completely  oxidized  and  that  the  iodine  solu- 
tion has  been  added  in  slight  excess.  Not  less  than 
20  cc.  of  decinormal  iodine  V.  S.  should  be  consumed 
before  the  blue  color  appears. 

The   reaction  is  illustrated   by  the   following  equa- 
tion : 

2(K(SbO)C4H40.)+H,0  +  2l9   +  3HaO 
4)662.42  4)506. 

10)165.605  IO)l£_6jJL  N 

16.5605  gms.  12.65  gnis.  or  1000  cc.  —  I.V.S. 

=  4HI  +  2KHC4H406  +  2HSb08. 

N 
Thus  each  cc.  of  —  iodine  V.  S.  represents  0.0165605 

gm.  of  pure  crystallized  tartar  emetic. 

2(K(SbO)C4H4O.)     (anhydrous). 
4)644.46 
10)161.115  N 

16.1115  gms.  =  12.65  gms.  of  iodine  or  1000  cc.  —  V.  S. 

N 
Thus  each  cc.  of  —  iodine  V.  S.  represents  0.0161115 

gm.  of  anhydrous  tartar  emetic.     Thus 

20  cc.  =  0.0165605  gm.  X  20  =  .33121  gm. ; 

0.33121  X  ioo 

-H -  =  100$  crystallized  salt ; 

0.331 
and 

0.0161 115  X  20  =  0.32223  gm. 

0.32223  X  ioo 

— * =  100$  anhydrous  salt. 

0.322  * 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       I? I 


The  operation  should  be  quickly  conducted  or  a 
precipitate  of  antimonous  hydrate  will  be  formed, 
upon  which  the  iodine  has  little  effect.  The  antimony 
must  be  in  solution  to  be  properly  attacked. 

TABLE  OF  SUBSTANCES   ESTIMATED   BY   IODINE. 


^J 

Name  of  Substance. 

Formula. 

It 

Factor. 

°^ 

Antimony    and      potassium  | 
tartrate  f 

2(K(SbO)C4H408)+H20 

662.42 

j  Cryst.      .016560 
1  Anhydr.  .016111 

Arsenic  trioxide  

As203 

197.68 

.004942 

Potassium  sulphite  

103.84 

Sodium  bisulphite    

2  NaSHSO32 

103.86 

.005193 

Sodium  sulphite     

NcioSOa  -4-  yHoO 

251.58 

.012579 

Sodium  thiosulphate    | 
(hyposulphite)  J 

Na2Sa03  +  5HaO 

247.64 

.024764 

Sulphur  dioxide     

SO, 

63  90 

Sulphurous  acid  

H2SO3 

81.86 

A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 


CHAPTER  XIII. 
ESTIMATION  OF  SUBSTANCES  READILY  REDUCED. 

ANY  substance  which  readily  yields  oxygen  in  a  defi 
nite  quantity,  or  is  susceptible  of  an  equivalent  action, 
which  involves  its  reduction  to  a  lower  quantivalence, 
may  be  quantitatively  tested,  by  ascertaining  how  much 
of  a  reducing  agent  of  known  power  is  required  by  a 
given  quantity  of  the  substance  for  its  complete  re- 
duction. 

The  principal  reducing  agents  which  may  be  em- 
ployed in  volumetric  analysis  are  sodium  thiosulpJiate, 
sulphurous  acid,  arsenous  acid,  oxalic  acid,  metallic 
zinc,  and  magnesium. 

The  sodium  thiosulphate  is  the  only  one  which  is 
employed  officially  in  the  U.  S.  P.  in  the  form  of  a 
volumetric  solution.  It  is  used  in  the  estimation  of 
free  iodine,  and  indirectly  of  other  free  halogens,  or 
compounds  in  which  the  halogen  is  easily  liberated,  as 
in  the  hypochlorites,  etc. 

This  method  of  analysis  is  called  lodometry. 

It  depends  upon  the  fact  that  iodine  is  an  indirect 
oxidizer,  as  shown  by  its  action  upon  water,  the  hydro- 
gen of  which  it  abstracts,  forming  hydriodic  acid,  thus 
liberating  the  oxygen  in  a  nascent  state. 

When  sodium  thiosulphate  acts  upon  iodine,  sodium 
tetrathionate  and  sodium  iodide  are  formed,  and  the 
solution  is  decolorized. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       173 

This  reaction  takes  place  in  definite  proportions:  one 
molecular  weight  of  the  thiosulphate,  absorbs  one 
atomic  weight  of  iodine. 

2NatSA  +  I,  =  2NaI  +  NaaS4O8- 

Chlorine  cannot  be  directly  titrated  with  the  thiosul- 
phate, but  by  adding  to  the  solution  containing  free 
chlorine  an  excess  of  potassium  iodide,  the  iodine  is 
liberated  in  exact  proportion  to  the  quantity  of  chlorine 
present,  atom  for  atom. 

Cl,  +  2KI  =  2KC1  +  I,. 

Then  by  estimating  the  iodine,  the  quantity  of 
chlorine  is  ascertained.  All  bodies  which  contain 
available  chlorine,  or  which  when  treated  with  hydro- 
chloric acid  evolve  chlorine,  may  be  estimated  by  this 
method. 

Also,  bodies  which  contain  available  oxygen,  and 
which  when  boiled  with  hydrochloric  acid  evolve 
chlorine,  such  as  manganates,  chromates,  peroxides,  etc., 
may  be  estimated  in  this  way. 

Solutions  of  ferric  salts,  when  acidulated  and  boiled 
with  an  excess  of  potassium  iodide,  liberate  iodine  in 
exact  proportion  to  the  quantity  of  ferric  iron  present. 

Thus  sodium  thiosulphate  may  be  used  in  the  esti- 
mation of  a  great  variety  of  substances  with  extreme 
accuracy. 

Preparation  of  Decinormal  Sodium  Thiosluphate 

(Hyposulphite),  Na2S203  + 5 H20-  |  ^>64   contains 
^24-74    (  gms.  in  I  litre. — Sodium  thiosulphate  is  a  salt 

of  thiosulphuric  acid  in  which  two  atoms  of  hydrogen 
have  been  replaced  by  sodium  ;  it  therefore  seems  that  a 


174       A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

normal  solution  of  this  salt  should  contain  one  half  the 
molecular  weight  in  grammes  in  one  litre. 

But  this  salt  is  used  chiefly  for  the  estimation  of 
iodine,  and,  as  stated  before,  one  full  molecular  weight 
reacts  with  and  decolorizes  one  atomic  weight  of  io- 
dine; and  since  one  atom  of  iodine  is  chemically  equiv- 
alent to  one  atom  of  hydrogen,  a  full  molecular  weight 
of  sodium  thiosulphate,  must  be  contained  in  a  litre  of 
its  normal  solution. 

Sodium  thiosulphate  is  easily  obtained  in  a  pure 
state,  and  therefore  the  proper  weight  of  the  salt,  re- 
duced to  powder  and  dried  between  sheets  of  blotting- 
paper,  maybe  dissolved  directly  in  water,  and  made  up 
to  one  litre. 

The  U.  S.  P.  directs  that  a  stronger  solution  than 
necessary  be  made,  its  titer  found  by  iodine,  and  then 
the  solution  diluted  to  the  proper  measure. 

30  gms.  of  selected  crystals  of  the  salt  are  dissolved 
in  enough  water  to  make,  at  or  near  15°  C.  (59°  F.) 
uoo  cc. 

Transfer  locc.  of  this  solution  into  a  flask  or  beaker, 
add  a  few  drops  of  starch  T.  S.,  and  then  gradually 
deliver  into  it  from  a  burette  decinormal  iodine  solu- 
solution,  in  small  portions  at  a  time,  shaking  the  flask 
after  each  addition,  and  regulating  the  flow  to  drops 
toward  the  end  of  the  operation.  As  soon  as  a  blue 
color  is  produced  which  does  not  disappear  upon  shak- 
ing, but  is  not  deeper  than  pale  blue,  the  reaction  is 
completed.  Note  the  number  of  cc.  of  iodine  solution 
used,  and  then  dilute  the  thiosulphate  solution  so  that 
equal  volumes  of  it  and  the  decinormal  iodine  V.  S. 
will  exactly  correspond  to  each  other,  under  the  above- 
mentioned  conditions. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       1/5 

Example.  —  The  10  cc.  of  sodium  thiosulphate,  we  will 
assume,  require  10.7  cc.  of  decinormal  iodine  V.  S. 

The  sodium-thiosulphate  solution  must  then  be 
diluted  in  the  proportion  of  10  cc.  to  10.7  cc.,  or  1000 
cc.  to  1070  cc. 

After  the  solution  is  thus  diluted  a  new  trial  should 
be  made,  in  the  manner  above  described,  in  which  50 
cc.  of  the  thiosulphate  solution  should  require  exactly 
50  cc.  of  the  decinormal  iodine  V.  S.  to  produce  a 
faint-blue  color. 

The  solution  should  be  kept  in  small  dark  amber- 
colored,  glass-stoppered  bottles,  carefully  protected 
from  dust  and  air. 

One  cc.  of  this  solution  is  the  equivalent  of  : 

Iodine  .....  .  ........  ...  0.012653  gramme. 

Bromine  ................  0.007976        " 

Chlorine  ..........  .  .....  0.003537        " 

Iron  in  ferric  salts  .......  0.005588        " 


Iodine,   1=   V*i'  —  Dissolve  0.32  gm.  of  iodine 

in  20  cc.  of  water,  in  a  beaker  or  flask,  with  the  aid 
of  i  gm.  of  potassium  iodide;  the  solution  is  mixed 
with  a  few  drops  of  starch  T.  S.,  and  then  the  deci- 
normal sodium  thiosulphate  V.  S.  gradually  delivered 
in  from  a  burette,  in  small  portions  at  a  time,  shaking 
the  flask  after  each  addition,  and  regulating  the  flow 
to  drops  toward  the  end  of  the  reaction,  until  a  final 
drop  just  discharges  the  blue  color. 

Note  the  number  of  cc.  of  decinormal  sodium  thio- 
sulphate V.  S.  consumed,  and  multiply  this  number  by 
the  factor  for  iodine. 


1 76       A   TEXT-BOOK   OP^   VOLUMETRIC   ANALYSIS. 

2(Na3S2O3  +  5H,O)  +  I,  =  Na2S4O6  +  2NaI  +  ioH,O. 
2)496  2)253 

10)248  10)126.5 

24.8  gms.  or  12.65  £ms' 

looo  cc.  —  V.  S. 
10 

Thus  the  factor  for  iodine,  that  is,  the  quantity  equiv- 

N 
alent  to  I  cc.  of   —  thiosulphate  V.  S.,  is  0.01265  gm. 

0.32  gm.  of  iodine,  which  answers  to  the  tests  of  the 

N 
U.  S.  P.,  requires  at  least  25  cc.  of  the  —  V.  S. 

0.01265  X  25  =  0.31625  gm. 

.31625  X  TOO 

-2-Cl      -  =  98.8$  pure  iodine. 

Liquor  lodi  Compositus  (Lugol's  Solution). — This 
is  an  aqueous  solution  of  iodine  and  potassium  iodide. 

It  is  estimated  for  iodine  in  the  same  way  as  the 
foregoing.  The  potassium  iodide  acts  merely  as  a  sol- 
vent for  free  iodine,  and  does  not  enter  into  the  re- 
action. 

10  or  12  gms.  of  the  solution  is  a  convenient  quan- 
tity to  operate  upon.  Starch  T.  S.  is  the  indicator. 

The  U.  S.  P.  states  that  12.66  gms.  of  the  solution 
should  require  for  complete  decoloration  from  49.3  to 
so  cc.  of  decinormal  sodium  thiosulphate  V.  S. 

N 
As  shown  by  the  above  equation,  each  cc.  of  the  — 

V.  S.  represents  0.01265  gm.  of  pure  iodine.     There- 
fore 50  cc.  represent  0.01265  X  50  =  .6325  gm. 

.6325  X  ioo 

=  5$  pure  iodine,  about. 


A  TEXT-BOOK   OF    VOLUMETRIC   ANALYSIS.       1 77 

Tinctura  lodi  (Tincture  of  Iodine). — This  is  an  al- 
coholic solution  of  free  iodine,  and  must  be  diluted 
with  a  solution  of  potassium  iodide,  before  titration,  in 
order  to  provide  sufficient  liquid  to  keep  the  resulting 
salts  in  solution. 

Aqua  Chlori  (Chlorine  Water) — This  is  an  aqueous 

solution  of  chlorine,  Cl  =   j  »?f      i  containing  at  least 

\          0  J'T" 

0.4$  of  the  gas. 

The  estimation  of  chlorine  is  effected  in  an  indirect 
way,  namely,  by  determining  the  quantity  of  iodine 
which  it  liberates  from  potassium  iodide. 

A  definite  quantity  of  chlorine  will  liberate  a  definite 
quantity  of  iodine  from  an  iodide  ;  these  quantities  are 
in  exact  proportion  to  their  atomic  weights,  as  the 
equation  shows : 

2KI  +  Cl,  =  2KC1  +  Ia 
2)70.74  2)253 

10)35.37  10)126.  s_ 

3-537  gms.  12.65  gms. 

Thus  it  is  seen  that  by  estimating  the  liberated  io- 
dine the  quantity  of  chlorine  may  be  determined  with 
accuracy. 

Ten  gms.  is  a  convenient  quantity  to  operate  upon. 
To  this  about  half  a  gramme  of  potassium  iodide  is 
added.  A  little  starch  T.  S.  is  then  introduced,  and 
the  titration  is  begun,  with  decinormal  sodium  thiosul- 
phate  V.  S. 

When  the  blue  color  of  starch  iodide  has  entirely 
tLs.ippeared  the  reaction  is  finished. 

The  reaction  between  iodine  and  sodium  thiosulphate 
is  illustrated  by  the  following  equation  * 


178      A   TEXT-BOOK   OF  VOLUMETRIC    ANALYSIS. 

I2  +  2(Na2SaOs  +  5H10) 

2)253  2)496 

10)126.5  10)248 

12.65  gms.  24.8  gms.  or  1000  cc.  — -  V.  S. 

10 


N 

Thus  we  see  that  1000  cc.  of—  Na2S,O3,5HaO  repre- 
sent 12.65  gms-  of  iodine,  which  are  equivalent  to  3.537 
gms.  of  chlorine. 

Each  cc.  therefore  is  equivalent  to  .003537  gm»  °f 
chlorine.  This  number  is  the  factor  which,  when  mul- 

N 
tiplied  by  the  number  of  cc.  of  —  thiosulphate  V.  S. 

used,  gives  the  weight  in  grammes  of  chlorine,  contained 
in  the  quantity  of  chlorine  water  acted  upon. 

The  U.  S.  P.  requirement  is  that  17.7  gms.  of  chlorine 
water,  when  mixed  with  I  gm.  of  potassium  iodide  dis- 

N 
solved  in  10  cc.  of  water,  and  titrated  with  --  sodium 

thiosulphate  V.  S.  should  consume  not  less  than  20  cc. 
of  the  latter  in  decolorizing  the  solution. 


•003  5 37  X  20  =  . 07074  gm 
.07074  X  ioo 


17.7 


of  chlorine. 


Chlorinated  Lime  (Calx  Chlorata,  Chloride  of  Lime, 
Bleaching-powder). — This  substance  was  formerly  sup- 
posed to  be  a  compound  of  lime  and  chlorine,  CaOCl3, 
and  hence  the  name  chloride  of  lime.  It  is  now  gener- 
ally considered  to  be  a  mixture  of  calcium  chloride  and 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.      179 

calcium  hypochlorite,  CaCl,  +  Ca(ClO),  or  2(CaOCla). 
The  hypochlorite  is  the  active  constituent.  This  is  a 
very  unstable  salt,  and  is  readily  decomposed  even  by 
carbonic  acid.  When  treated  with  hydrochloric  acid  it 
gives  off  chlorine. 

The  value  of  chlorinated  lime  as  a  bleaching  or  dis- 
infecting agent  depends  upon  its  available  chlorine, 
that  is,  the  chlorine  which  the  hypochlorite  yields 
when  treated  with  an  acid. 

In  estimating  the  available  chlorine,  the  latter  is 
liberated  with  hydrochloric  acid.  This  liberated  gas, 
then,  acting  upon  potassium  iodide,  sets  free  an  equiva- 
lent amount  of  iodine.  The  quantity  of  iodine  is  then 
determined,  and  thus  the  amount  of  available  chlorine 
found.  .1  to  .2  gm.  is  a  convenient  quantity  to  oper- 
ate upon. 

The  U.  S.  P.  directs  to  weigh  off  ^0.35  (0.354)  gm.  of 
chlorinated  lime.  This  is  to  be  thoroughly  triturated 
with  50  cc.  of  water  and  carefully  transferred,  together 
with  the  washings  into  a  flask.  0.8  gm.  or  more  of  po- 
tassium iodide  and  5  cc.  of  diluted  hydrochloric  acid  are 
then  added,  and  into  the  resulting  reddish-brown  liquid, 

N 
the  —  sodium  thiosulphate  V.  S.  is  delivered  from  a 

burette.  Towards  the  end  of  the  titration,  when  the 
brownish  color  of  the  liquid  is  very  faint,  a  few  drops 
of  starch  T.  S.  are  added  and  the  titration  continued 
until  the  bluish  or  greenish  color  produced  by  the 
starch  has  entirely  disappeared.  Not  less  than  35  cc. 
of  the  volumetric  solution  should  be  required  to  pro- 
duce this  result. 

The  reactions  which  take  place  in  this  process  are 
illustrated  by  the  following  equations  : 


180      A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

,  +  4HC1  =  2CaCla  +  2HaO  +  2C19 


2da  +  4KI  =  4KC1  +  2lf. 
4)141-48  4)506 

10)  35-37  10)126.5 

3-537  gms.  12.65  gms. 


2la 

40)506 


12.65  gins.        24.8  gms.  or  1000  cc.  —  thiosulphate  V.  S. 


We  thus  see  that  I  cc.  of  the  decinormal  volu- 
metric solution  represents  0.01265  gm.  of  iodine,  which 
is  equivalent  to  0.003537  gm-  °f  available  chlorine. 
Then 

0.003537  X  35  =  o.i237grgm. 
0.12379  x  ioo 


•35 


=  35$  of  available  chlorine. 


This  is  a  very  rapid  method  for  estimating  chlorine  ; 
but  when  calcium  chlorate  is  present  in  the  bleaching- 
powder  (and  it  often  is,  through  imperfect  manufact- 
ure) the  chlorine  from  it,  is  recorded,  as  well  as  that 
from  the  hypochlorite,  the  chlorate  being  decomposed 
into  chlorine,  etc.,  by  hydrochloric  acid.  The  chlorate, 
however, is  of  no  value  in  bleaching;  its  chlorine  is  not 
available.  Hence,  unless  the  powder  is  known  to  be 
free  from  chlorate,  the  analysis  should  be  made  by 
means  of  arsenous-acid  solution. 

The  Arsenous-acid  Process.  —  0.35  gm.  of  the 
bleaching-powder  is  rubbed  to  a  smooth  paste  with  50 
cc.  of  water,  as  described  above.  A  measured  excess 
of  decinormal  arsenous  acid  V.  S.  is  then  added  ;  this 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       l8l 

is  followed  by  a  little  starch  T.  S.,  and  then  decinormal 
iodine  V.  S.  added  until  the  blue  color  appears.  De- 
duct the  number  of  cc.  of  the  standard  iodine  solution 
used  from  those  of  standard  arsenous-acid  solution, 
and  the  quantity  of  the  latter  which  went  into  combi- 
nation is  found. 

N 
Each  cc.  of  —  As,O,  V.  S.  represents  .003537  gm-  °f 

available  chlorine. 

2CaOCl,  +     As2O3  =  As2O6  +  2CaCl, 
4)141-48  4)198 

10)  35-37  10)  49-5  N 

3-537  gms.          4.95  gms.  or  1000  cc.  —^  V.  S. 

Decinormal  Arsenous-acid  Solution  is  made  by 
dissolving  4.95  gms.  of  the  purest  sublimed  arsenous 
anhydride  (As,O,)  in  about  250  cc.  of  distilled  water 
with  the  aid  of  about  20  gms.  of  pure  potassium  bicar- 
bonate. The  acid  should  be  in  fine  powder,  and  the 
mixture  warmed,  to  effect  complete  solution. 

The  solution  is  checked  with  decinormal  iodine  V.  S., 
using  starch  as  indicator. 

Decinormal  arsenous-acid  solution  and  decinormal 
iodine  solution  should  correspond,  volume  for  volume. 

Liquor  Sodae  Chloratae  (Solution  of  Chlorinated 
Soda ;  Labarraque's  Solution). — This  is  an  aqueous 
solution  of  several  chlorine  compounds  of  sodium, 
principally  sodium  chloride  and  hypochlorite,  contain- 
ing at  least  2.6$  of  available  chlorine. 

In  this  solution,  as  in  chlorinated  lime,  it  is  the 
available  chlorine  which  is  estimated.  The  chlorine  is 
first  liberated  with  hydrochloric  or  sulphuric  acid  ;  this 
then  liberates  iodine  from  potassium  iodide,  and  the 


1 82       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

free  iodine  is  then  determined  by  standard  solution  of 
thiosulphate. 

^6.7  (6.74)  gms.  of  chlorinated  soda  solution  are 
mixed  with  50  cc.  of  water,  2  gms.  of  potassium  iodide, 
and  10  cc.  of  hydrochloric  acid,  together  with  a  few 
drops  of  starch  T.  S.  Then  pass  into  the  mixture  from 
a  burette  sufficient  decinormal  sodium  thiosulphate 
V.  S.  to  just  discharge  the  blue  or  greenish  tint  of  the 
liquid. 

The  reaction  is  illustrated  by  the  following  equation. 
Hydrochloric  acid  liberates  chlorine  from  the  salts  in 
the  solution : 

NaCl,NaC10  +  2HC1  =  2NaCl  +  HaO  +  Cla. 

70.74 

The  chlorine  then  liberates  iodine  from  potassium 
iodide: 

Cla   +   2KI  =  2KC1  +  I,. 
20)70.74  20)253 

3-537  12.65 

The  iodine  is  then  determined  by  sodium  thiosul- 
phate V.  S. : 

I,   +  2(NaaS2O3+5HaO)=2NaI+NaaS4Ofl+ioH20. 
2)253  2)496 

10)126.5  10)248 

12.65  gms.  24.8  gms.  or  1000  cc.  —  V.  S. 

Thus  each  cc.  of  standard  solution  represents  .01265 
gm.  of  iodine,  which  is  equivalent  to  .063537  gm.  of 
available  chlorine. 

In  practice  the  potassium  iodide  should  always  be 
added  before  the  hydrochloric  acid  is,  so  that  the 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       183 

chlorine  has  potassium  iodide  to  act  upon,  as  soon  as 
it  is  itself  liberated,  and  thus  any  loss  of  chlorine  is 
obviated. 

In  the  pharmacopceial  test  above  given  not  less  than 

CO  cc.  of  the  —  V.  S.  should  be  required. 
10 

0.003537  X  50  =  0.17785  gm. 

0.17785  X  IPO  =  2>6^  available  ci. 
6.7 

Instead  of  weighing  off  the  U.  S.  P.  quantity,  any 
other  convenient  weight  may  be  taken. 

ESTIMATION   OF  FERRIC   SALTS. 

When  a  ferric  salt  in  an  acidulated  solution  is  di- 
gested with  an  excess  of  potassium  iodide  the  salt  is 
reduced  to  the  ferrous  state,  and  iodine  is  set  free. 

Fe2Cl6  +  2KI  =  2FeCl3  +  2KC1  +  I2. 

One  atom  of  iodine  is  liberated  for  each  atom  of 
iron  in  the  ferric  state.  The  liberated  iodine  is  then 
determined  by  sodium  thiosulphate,  in  the  usual  way. 
12.65  gms.  of  iodine  =  5.6  gms.  of  metallic  iron. 

This  is  the  method  of  the  U.  S.  P.  ;  it  is  given  in 
detail  here. 

^0.56  (0.5588)  gm.  of  the  salt  is  dissolved  in  10  or  15 
cc.  of  water  and  2  cc.  of  hydrochloric  acid  in  a  glass- 
stoppered  bottle  having  a  capacity  of  about  100  cc. 
i  gm.  of  potassium  iodide  is  then  added,  and  the  mix- 
ture digested  for  half  an  hour  at  a  temperature  of  40°  C. 
(104°  F.).  During  the  digestion  the  stopper  should  be 


1 84      A  TEXT-BOOK   OF  VOLUME-TRIG   ANALYSIS. 

left  in  the  bottle,  and  the  heat  not  allowed  to  rise  too 
high,  otherwise  the  liberated  iodine  will  be  volatilized. 
When  cool  a  few  drops  of  starch  T.  S.  are  added. 

N 

It  is  now  ready  for  titrating  with  —  sodium  thiosul- 

10 

phate.  Each  cc.  corresponds  to  I  per  cent,  of  metallic 
iron. 

When  the  quantity  of  metallic  iron  and  the  chemical 
formula  for  the  ferric  salt  under  estimation  are  known, 
the  quantity  of  pure  salt  is  easily  found  by  calculation. 

In  all  the  estimations  of  ferric  iron  it  is  convenient 
to  take  0.56  gm.  of  the  salt.  Each  cc.  of  the  volumetric 
solution  used  will  then  represent  \<f>  of  metallic  iron, 
assuming  the  atomic  weight  of  iron  to  be  56. 

Ferric  salts  may  be  tested  in  many,  other  ways ;  for 
instance: 

A  ferric  salt  in  solution  may  be  filtered  through  a 
column  of  zinc  dust,  which  reduces  it  to  the  ferrous 
state.  This  is  then  estimated  with  potassium  perman- 
ganate V.  S.  in  the  usual  method,  or  the  ferric  solution 
is  treated  with  a  few  small  pieces  of  zinc  or  magnesium 
coarsely  powdered,  until  complete  reduction  is  effected. 
When  a  red  color  is  no  longer  produced  by  sulphocy- 
anate  of  potassium  the  ferric  salt  is  completely  re- 
duced, and  may  be  estimated  with  potassium  perman- 
ganate V.  S. 

Stannous  chloride,  ammonium  bisulphite,  and  other 
substances  may  also  be  used  as  reducing  agents. 

Ferric    Chloride,     Fe2Cl6  +  I2H2O  ==    j  J39'5 .— 

(    54°-4 

^0.56  (0.5588)  gm.  of  the  salt  is  dissolved  in  a  glass- 
stoppered  bottle  (having  a  capacity  of  about  100  cc.) 
in  10  cc.  of  water  and  2  cc.  of  hydrochloric  acid,  and 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.      185 

after  the  addition  of  I  gm.  of  potassium  iodide,  is  kept 
for  half  an  hour  at  a  temperature  of  40°  C.  (104°  F.), 
then  cooled,  mixed  with  a  few  drops  of  starch  T.  S., 
and  titrated  with  decinormal  sodium  thiosulphate  V.  S. 
until  the  blue  or  greenish  color  of  the  liquid  is  dis- 
charged. Each  cc.  represents  ^0.0056  gm.  or  \%  of 
metallic  iron,  or  0.026975  gm.  of  pure  ferric  chloride. 
The  following  equations  illustrate  the  reactions: 

Fe2ClB+i2H2O+2KI  =  2FeCl2-[-  2KC1  +  I,  +  I2H2O. 


20)539-5  20)253 

26.975  gms.  12.65  gms- 


Then 


2(NaiS10I 


20)253          20)496  N 

12.65  gms.          24.8  gms.  or  1000  cc.  —  V.  S. 

10 

=  2NaI  +  Na2S4O6  +  ioH2O. 

20  cc.  of  the  —  V.  S.  should  be  required,  which  rep- 
10 

resents  20$  of  metallic  iron,  or  96.34$  of  pure  ferric 
chloride  (crystallized)  : 

0.026975  X  20  =    0.5395  gm. 
=  93- 


Liquor  Ferri  Chloridi  (Solution  of  Ferric  Chloride). 
—  This  is  an  aqueous  solution  of  ferric  chloride,  Fe2Cl6 

=  |  *  >  containing  about  37.8  per  cent,  of  the  an- 

hydrous salt  or  about  13  per  cent,  of  metallic  iron. 


1 86     A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

0.56  (or  .5588)  gm.  of  the  solution  is  introduced  into 
a  glass-stoppered  bottle  (having  a  capacity  of  about 
100  cc.),  together  with  1 5  cc.  of  water  and  2  cc.  of  hydro- 
chloric acid,  i  gm.  of  potassium  iodide  is  then  added, 
and  the  mixture  kept  for  half  an  hour  at  40°  C.  (104° 
F.),  then  cooled,  and  mixed  with  a  few  drops  of  starch 

N 
T.  S.  and  titrated  with  -  -  sodium  thiosulphate  V.  S. 

until  the  blue  or  greenish  color  of  the  liquid  is  dis- 
charged. 0.56  gm.  of  the  solution  having  been  taken, 
each  cc.  of  the  standard  solution  represents  I  per  cent, 
and  13  cc.  should  be  required.  If  1.12  gms.  are  taken, 
as  the  U.  S.  P.  directs,  each  cc.  represents  0.5  per  cent, 
and  26  cc.  should  be  required.  The  reactions  are  the 
same  as  in  ferric  chloride,  each  cc.  representing 
0.026975  gm.  of  crystallized  ferric  chloride,  or  0.016199 
gm.  of  anhydrous  ferric  chloride,  or  .0056  gm.  of  metal- 
lic iron.  To  find  percentage :  Multiply  by  number  of 
cc.  used,  then  multiply  the  result  by  100  and  divide  by 
the  quantity  of  solution  taken. 

Tinctura  Ferri  Chloridi  (Tincture  of  Ferric  Chlo- 
ride).— A  hydro-alcoholic  solution  of  ferric  chloride, 

FeaCl6  =  |  •*?Jr?  >   containing  about    13.6   per  cent. 

of  anhydrous  ferric  chloride,  and  corresponding  to 
about  4.7  (4.69)  per  cent,  of  metallic  iron. 

To  estimate  this  tincture  follow  the  directions  given 
for  liquor  ferri  chloridi. 

Ferric    Citrate,     Fe,(C.H.OT).  =  )  ,^;4*.-*o.56 

(0.5588)  gm.  of  the  salt  is  dissolved  in  a  glass-stop- 
pered bottle  (having  a  capacity  of  100  cc.)  in  15  cc.  of 
water  and  2  cc.  of  hydrochloric  acid,  with  the  aid  of 
gentle  heat.  I  gm.  of  potassium  iodide  is  then  added, 


A  TEXT-BOOK  OF   VOLUMETRIC   ANALYSIS.       187 

and  the  mixture  kept  for  half  an  hour  at  a  temperature 
of  40°  C.  (104°  F.).  It  is  then  cooled,  and  a  few  drops 
of  starch  T.  S.  added.  The  decinormal  sodium  thio- 
sulphate  V.  S.  is  then  delivered  in  from  a  burette,  until 
the  blue  or  greenish  color  of  the  liquid  just  disappears. 
Each  cc.  of  the  decinormal  solution  represents  I  per 
cent,  or  0.0056  gm.  of  metallic  iron,  corresponding  to 
0.024424  gm.  of  ferric  citrate. 

3Fe,(C.HiO,),+6KI=2Fes(C.H(0,),+2K8C,H.O,+3l,. 

Ferric  citrate.  Ferrous  citrate.  s 

3Fe2  \488.48 


6)335.28  3  10)126.5 

10)  55-88        6)1465.44  12.65 

5.588  gms.  10)  244.24 
(*5.6  gms.)        24.424  gms. 

!,.+  2(Na2S203,  5HaO)  =  2NaI+Na2S406+  ioH20. 
2)253  2)496 

10)126.5  10)248 

12.65  gms-  24-8  gms.  or  looo  cc.  —  sodium  thiosulphate. 

Thus  each  cc.  represents  0.01265  gm.  of  iodine,  which 
corresponds  to  0.024424  gm.  of  ferric  citrate  or  ^0.0056 
gm.  metallic  iron. 

16  cc.  =  16  X  0.0056  =  .0896  gm.  metallic  iron. 

.0896  X  IPO  =  l6  , 

0.56 

16  X  0.024424  =  0.390784  gm.  ferric  citrate. 
0.390784  X  IPO  =  6       , 
0.56 

Liquor  Ferri  Citratis  (Solution  of  Ferric  Citrate). 
—This  is  an  aqueous  solution  of  ferric  citrate,  corre- 
sponding to  about  7.5  per  cent,  of  metallic  iron. 


188      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

^0.56  (0.5588)  gm.  of  the  solution  is  introduced  into 
a  glass-stoppered  bottle  (having  a  capacity  of  about 
IOO  cc.),  together  with  I  5  cc.  of  water  and  2  cc.  of  hy- 
drochloric acid,  i  gm.  of  potassium  iodide  is  then 
added,  and  the  mixture  kept  at  a  temperature  of  40° 
C.  (104°  F.)  for  half  an  hour;  it  is  then  cooled  and 
mixed  with  a  few  drops  of  starch  T.  S.,  and  deci- 
normal  thiosulphate  V.  S.  delivered  in  from  a  burette 
until  the  blue  or  greenish  color  of  the  liquid  is  dis- 
charged. Each  cc.  of  the  volumetric  solution  indicates 
\%  of  metallic  iron.  If  *I.I2  (1.1176)  gms.  of  the 
liquor  are  taken,  as  the  U.  S.  P.  directs,  each  cc.  of  the 
V.  S.  used  represents  0.5$  of  metallic  iron. 

Iron  and  Ammonium  Citrate  (Ferri  et  Ammonii 
Citras). — The  precise  chemical  constitution  of  this 
preparation  is  not  determined.  Therefore  the  metallic 
iron  only  is  estimated,  of  which  it  should  contain  16 
per  cent. 

Ammonio-ferric  Tartrate  (Ferri  et  Ammonii  Tar- 
tras). — The  exact  chemical  composition  of  this  com- 
pound is  not  known.  It  is,  theoretically,  2(FeO)- 
NH4C4H4O6.3H2O).  It  should  contain  17  per  cent,  of 
metallic  iron. 

Potassio-ferric  Tartrate  (Ferri  et  Potassii  Tartras). 
— There  is  some  difference  of  opinion  as  to  the  com- 
position of  this  salt.  It  is  probably  a  double  salt,  con- 
sisting of  one  molecule  of  ferric  tartrate,  Fea(C4H4Oe)3 
and  one  of  potassium  tartrate,  K2C4H4O6,  with  one  of 
H2O.  It  should  contain  15  per  cent,  of  metallic  iron. 

Soluble  Ferric  Phosphate  (Ferri  Phosphas  Solu- 
bilis). — This  salt  is  called  soluble  ferric  phosphate  in 
order  to  distinguish  it  from  the  true  ferric  phosphate. 
It  is  not  a  definite  chemical  compound,  but  a  mixture 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.       189 

of  citrate  and  phosphate  of  sodium  and  iron  It  should 
contain  12  per  cent  of  metallic  iron. 

The  foregoing  four  salts  being  of  indefinite  chemical 
composition,  are  tested  for  metallic  iron  only,  as 
follows  : 

°-56  (0.5588)  gm.  of  the  salt  is  dissolved  in  a  glass- 
stoppered  bottle  (having  a  capacity  of  100  cc.)  in  15  cc. 
of  water  and  2  cc.  of  hydrochloric  acid.  I  gm.  of  po- 
tassium iodide  is  then  added,  and  the  mixture  kept  at 
40°  C.  (104°  F.)  for  half  an  hour,  then  cooled,  a  few 
drops  of  starch  T.  S.  added,  and  decinormal  sodium 
thiosulphate  V.  S.  delivered  in  slowly  from  a  burette 
until  the  blue  or  greenish  color  of  the  liquid  is  com- 

N 
pletely  discharged.     Each  cc.  of  —  V.  S.  represents  I 

per  cent,  of  metallic  iron,  if  0.56  (0.5588)  gm.  of  the 
salt  is  taken. 

Iron  and  Quinine  Citrate  (Ferri  et  Quininae  Cit- 
ras). — The  U.  S.  P.  gives  an  assay  process  for  quinine 
and  one  for  iron  to  be  applied  to  this  salt* 

ESTIMATION   OF  THE   QUININE. 

1. 12  (1.1176)  gms.  of  the  salt  are  dissolved  in  a  capsule 
in  20  cc.  of  water,  with  the  aid  of  gentle  heat. 

The  solution  is  poured  into  a  separator,  the  capsule 
is  rinsed  with  a  little  water,  and  the  rinsings  added  to 
the  liquid  in  the  separator ;  when  this  has  become  cool, 
add  5  cc.  of  ammonia  water  and  10  cc.  of  chloroform, 
and  shake.  Allow  the  liquids  to  separate,  draw  off  the 
chloroformic  layer,  and  add  to  the  residual  liquid  a 
second  and  a  third  portion  of  10  cc.  of  chloroform 
added,  shaking  after  each  addition,  and  drawing  off  the 
chloroformic  solution.  The  combined  chloroformic 


A   TEXT-BOOK   OF    VOLUMETRIC   ANALYSIS. 

solutions  are  evaporated  spontaneously  in  a  tared  cap- 
sule, and  the  residue  dried  at  100°  C.  (212°  F.)  to  a 
constant  weight.  It  should  weigh  not  less  than  0.1288 
gm. 

0.1288  X  TOO 


1.1176 


=  11.5$  of  dried  quinine. 


In  the  above  assay  the  ammonia  water  precipitates 
the  quinine  and  the  chloroform  dissolves  it.  Then  by 
evaporating  the  chloroformic  solution  the  quinine  is 
obtained. 

ESTIMATION    OF    THE    IRON. 

The  aqueous  liquid  from  which  the  quinine  has  been 
removed,  as  above  described,  is  heated  on  a  water-bath 
until  the  odor  of  chloroform  and  ammonia  has  disap- 
peared; allow  the  liquid  to  cool,  and  dilute  it  with  water 
to  the  volume  of  50  cc.  Take  25  cc.  of  this,  put  it  in  a 
glass-stoppered  bottle  (having  a  capacity  of  100  cc.), 
add  2  cc.  of  hydrochloric  acid  and  I  gm.  of  potassium 
iodide,  and  digest  at  40°  C.  (104°  F.)  for  half  an  hour. 
Allow  it  to  cool,  add  a  few  drops  of  starch  T.  S.  and 
titrate  with  decinormal  sodium  thiosulphate  V.  S.  until 
the  blue  or  greenish  color  is  discharged. 

Each  cc.  of  the  volumetric  solution  represents  0.0056 
(.005588)  gm.  of  metallic  iron,  or  I  per  cent.  14.5  cc, 
should  be  required. 

0.0056  X  14.5  =  0.0812  gm. 
0.0812  X  IPO  _          ^ 
0.56 

Soluble  Citrate  of  Iron  and  Quinine  (Ferri  et 
Quininae  Citras  Solubilis). — This  salt  is  assayed  for 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS,       19! 

quinine  and  iron  in  the  manner  above  described  under 
Ferri  et  Quinince  Citras,  and  should  respond  to  the 
requirements  for  the  latter. 

Iron  and  Strychnine  Citrate  (Ferri  et  Strychninae 
Citras). — This  salt  should  be  tested  quantitatively  for 
strychnine  and  iron. 

ESTIMATION   OF   THE   STRYCHNINE. 

*2.24  (2.2352)  gms.  of  the  salt  are  dissolved  in  a  sep- 
arator in  15  cc.  of  water,  5  cc.  of  ammonia  water  are 
then  added  and  10  cc.  of  chloroform,  and  the  mixture 
shaken.  Set  aside  so  as  to  allow  the  liquids  to  separate, 
draw  off  the  chloroformic  layer,  add  a  second  and  a 
third  portion  of  10  cc.  of  chloroform,  shaking  each 
time  and  drawing  off  the  chloroformic  solution.  The 
chloroformic  extracts  are  then  mixed,  and  allowed  to 
evaporate  spontaneously  in  a  tared  capsule.  The  resi- 
due is  then  dried  at  100°  C.  (212°  F.)  to  a  constant 
weight. 

This  residue  should  not  weigh  less  than  0.02  gm.  nor 
more  than  0.0224  gm.,  corresponding  to  not  less  than 
0.9  nor  more  than  i  per  cent,  of  strychnine. 

.0224  X  IQO  _      , 
2.24 

ESTIMATION   OF  THE   IRON. 

The  aqueous  liquid  from  which  the  strychnine  has 
been  removed  in  the  manner  described  above,  is  heated 
on  a  water-bath  until  the  chloroform  and  ammonia  are 
entirely  volatilized.  This  is  then  allowed  to  cool,  and 
diluted  with  water  to  the  volume  of  100  cc.  25  cc.  of 


I  Q2       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

this  are  transferred  to  a  glass-stoppered  bottle  (having  a 
capacity  of  100  cc.),  2  gms.  of  hydrochloric  acid  and  I 
gm.  of  potassium  iodide  are  then  added,  and  the  mix- 
ture kept  at  a  temperature  of  40°  C.  (104°  F.)  for  half 
an  hour.  After  it  has  been  allowed  to  cool  add  a  few 
drops  of  starch  T.  S.,  and  titrate  with  decinormal  so- 
dium  thiosulphate  V.  S.  until  the  blue  or  greenish  color 

N 
of  the  liquid  is  entirely  discharged.     16  cc.  of  the  — 

V.  S.  should  be  required  to  produce  this  result,  each  cc. 
corresponding  to  I  per  cent,  or  0.0056  gm.  of  metallic 
iron. 

0.0056  x  1  6  =  0.0896  gm. 
ao896  *  I0°  =  ,6*  of  Fe. 

O.5O 

Ammonio-ferric  Sulphate  (Ferri  et  Ammonii  Sul- 
phas ;     Ammonio-ferric    Alum),     Fe2(SO4)3.(NH4)3SO4 

2'1.—  This  salt  has  a  definite  chemical 


24H2O  =  | 


composition,  and  therefore  by  determining  the  quan- 
tity of  metallic  iron  the  quantity  of  pure  salt  may  be 
found  by  calculation. 

The  U.  S.  P.  process  for  assay  is  as  follows  : 
0.56  (0.5588)  gm.  of  the  salt  is  dissolved  in  a  glass- 
stoppered  bottle  (having  a  capacity  of  100  cc.)  in  15  cc. 
of  water  and  2  cc.  of  hydrochloric  acid,  I  gm.  of  potas- 
sium iodide  is  then  added,  and  the  mixture  kept  at  a 
temperature  of  40°  C.  (104°  F.)  for  half  an  hour.  It  is 
then  allowed  to  cool,  and  mixed  with  a  few  drops  of 
starch  T.  S.,  and  titrated  with  decinormal  sodium  thio- 
sulphate V.  S.  until  the  blue  or  greenish  color  of  the 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       193 

N 
liquid  is  discharged.     Not  less  than  n.6  cc.  of  the  — 

V.  S.  should  be  required,  each  cc.  corresponding  to 
i  per  cent,  or  .0056  gm.  of  metallic  iron,  or  0.0482  gm. 
of  the  salt.  See  the  following  equations  : 

(Fe,)    Fe.(SO)),(NH.)aSO,24HiO  +  3KI 

2)112  2)*g64 

10)  56  10)  482 

5.6  gms.  48.2  gms. 


S04    +    I2    +    24HaO. 

2)253 
10)126.5 

12.65  gms. 
Then 

I2    +    2(Na9SaO8.5H2O)=2NaI+NaaS406+ioH3O. 

2)253  2)496 

10)126.5  10)248 

12.65  gms.  24.8  gms.  or  1000  cc.  —  V.  S. 

10 

N 
Thus  it  is  seen  that  I  cc.  of  —  V.  S.  represents  0.01265 

gm.  of  iodine,  and  this  corresponds  to  0.0482  gm.  of 
ammonio-ferric  sulphate,  or  0.0056  gm.  of  metallic 
iron. 

0.0482  X  n.6  =  0.55912  gm. 

^  99^  of  the  pure  salt. 


0.0056  X  1  1.6  =  .06496  gm. 
*X 


194       A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

Soluble  Ferric  Pyrophosphate  (Ferri  Pyrophos- 
phas  Solublilis).  —  This  is  estimated  according  to  the 
U.  S.  P.  in  the  following  manner: 

0.56  (0.5588)  gm.  of  the  salt  is  dissolved  in  a  glass- 
stoppered  bottle  (having  a  capacity  of  100  cc.)  in  10  cc 
of  water,  then  10  cc.  of  hydrochloric  acid  and  subse- 
quently 40  cc.  of  water  are  added.  Then  I  gm.  of 
potassium  iodide  is  put  into  the  solution  and  the  tem- 
perature kept  at  40°  C.  (104°  F.)  for  half  an  hour.  The 
liquid  is  then  cooled  and  a  few  drops  of  starch  T.  S. 

N 
added,  and  the  —  sodium  thiosulphate  V.  S.  delivered 

in  from  a  burette,  until  the  blue  or  greenish  color  is 

N 
completely  discharged.     Each  cc.  of  the  —  V.  S.  repre- 

sents I  per  cent,  or  0.0056  gm.  of  metallic  iron. 

True  ferric  pyrophosphate  has  the  chemical  compo- 
sition Fe4(P2O7)3  -f-  9H2O.  The  soluble  ferric  pyro- 
phosphate of  the  U.  S.  P.  is  a  mixture  of  ferric  pyro- 
phosphate and  sodium  citrate. 

The  reaction  with  potassium  iodide  is  expressed  as 
follows  : 


4)746  4)506 

10)186.5  10)126.5 

18.65  gms.  12.65  gms. 

Thus   18.65  gms.  of  ferric  pyrophosphate  cause  the 
liberation  of  12.65  gms.  of  iodine,  and  since  each  cc.  of 

N 
-  sodium    thiosulphate  V.   S.   will  absorb,   and    con- 

sequently  represent,   .01265   gm.  of    iodine,    it   corre- 
sponds to  0.01865  gm.  of  pure  ferric  pyrophosphate. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       195 

10  cc.  of  the  decinormal  solution  is  the  quantity 
which  the  U.  S.  P.  requires  should  be  used. 

0.01865  X  10  =  0.1865  gm. 
0.1865  X  IOO  _ 

-- 


of  ferric  pyrophosphate,  which  corresponds  to  10$  of 
metallic'  iron  in  the  U.  S.  P.  salt. 

Ferric  Valerianate  (Ferri  Valerianas),  Fe2(C5H9Oa)6 
'=  {*7i8.  —  The  true  ferric  valerianate  is  illustrated  by 
the  above  formula,  but  the  U.  S.  P.  salt  is  of  variable 
composition,  and  should  contain  not  less  than  1556,  nor 
more  than  20$,  of  iron  in  combination. 

The  estimation  is  conducted  as  follows  :  *o.56(o.5588) 
gm.  of  the  salt  is  dissolved  in  a  glass-stoppered  bottle 
(having  a  capacity  of  100  cc.)  in  2  cc.  of  hydrochloric 
acid.  This  decomposes  the  salt,  forming  ferric  chlo- 
ride and  liberating  valerianic  acid.  15  cc.  of  water  are 
now  added,  together  with  I  gm.  of  potassium  iodide, 
and  the  mixture  heated  to  40°  C  (104°  F.)  and  kept  at 
that  temperature  for  half  an  hour;  it  is  then  cooled, 
and  the  liberated  iodine  estimated  with  decinormal 
sodium  thiosulphate  V.  S.,  using  starch  T.  S.  as  indi- 
cator. 

N 
Not  less  than  15  cc.  nor  more  than  20  cc.  of  the  - 

10 

V.  S.  should  be  required  to  discharge  the  color  of 
starch  iodide.  Each  cc.  corresponds  to  i$  of  metallic 
iron.  The  reactions  are  expressed  by  the  following 
equations: 

Fe,(C6H.O,),  +  6HC1  =  Fe,Cl.  +  6HC,H,O,;  .     .     (i) 


196      A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

Fe3Cl6  +  2KI  =  2FeCl2  +  2KC1  +  I,  ;  .     .     (2) 
I.+XNa.SA-SH.O)  -  2NaI  +  Na2S4O6+  ioH3O.  (3) 

Liquor  Ferri  Acetatis  (Solution  of  Ferric  Acetate). 
—  This  is  an  aqueous  solution,  containing  about  31$  of 

anhydrous  ferric  acetate  (Fe2(C2H3O2)6  =  j  *4^'92,  cor- 

responding to  7.5$  of  iron.  1.12  (1.1176)  gms.  of  the 
solution  are  introduced  into  a  glass-stoppered  bottle 
(having  a  capacity  of  100  cc.),  together  with  15  cc.  of 
water  and  2  cc.  of  hydrochloric  acid. 

I  gm.  of  potassium  iodide  is  then  added  and  the 
mixture  kept  at  a  temperature  of  40°  C.  (104°  F.)  for  half 
an  hour;  then  cooled,  and,  after  adding  a  few  drops  of 
starch  T.  S.,  pass  into  it  from  a  burette  decinormal 
sodium  thiosulphate  V.  S.  until  the  blue  or  greenish 
color  of  the  liquid  has  completely  disappeared. 

Each  cc.  of  the  decinormal  solution  thus  consumed 
represents  0.5$  of  metallic  iron. 

If  0.56  (0.5588)  gm.  of  the  solution  is  used  instead 
of  1.  12  (1.1176)  gm,,  and  treated  as  described  above, 

N 
each  cc.  of  the  —  V.  S.  represents  i<f>  of  metallic  iron, 

or  0.0056  gm. 

The  principal  reaction  is  expressed  by  the  following 
equation: 


Fe,(C,H30,). 

=  2Fe(C,H  ,0,),  +  2KC.H.O,  +  I, 

2)464.92  2)253 

10)232.46  10)126.5 

23.246  gms.  12.65  gms, 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.       197 

N 
Thus  each  cc.  of  the  —  V.  S.  also  represents  0.023246 

gm.  of  ferric  acetate. 

N 
15  cc.  of  the  --  V.  S.  should  be  required  if  1.12  gms. 

of  solution  are  taken. 

0.023246  X  15  =0.34869  gm. 
0.34869  X  ioo 


1. 12 


=  31.1$  of  ferric  acetate. 


N 
7.5  cc.  the  --  V.  S.  should  be  consumed  if  0.56  gm. 

is  taken. 

0.023246  X  7.5  =  0.17434  gm. 


o.i  7434  X  IQQ^          . 
0.56 

Liquor  Ferri  Nitratis  (Solution  of  Ferric  Nitrate). 
—  An  aqueous  solution  containing  about  6.2$  of  anhy- 

drous ferric  nitrate  (Fea(NO3)8  =  j  *  gl*   '  anc*  corre" 

spending  to  about  1.4$  of  metallic  iron. 

Introduce  into  a  glass-stoppered  bottle  (having  a 
capacity  of  ioo  cc.)  1.12  (1.1176)  gms.  of  the  solution, 
together  with  15  cc.  of  water  and  2  cc.  of  hydrochloric 
acid.  Then  add  to  the  mixture  I  gm.  of  potassium 
iodide,  and  keep  it  at  a  temperature  of  40°  C.  (104°  F.) 
for  half  an  hour.  Allow  the  mixture  to  cool,  and  esti- 
mate the  liberated  iodine  with  decinormal  sodium  thio- 
sulphate  V.  S.,  using  starch  T.  S.  as  indicator.  When 
the  blue  or  greenish  color  of  starch  iodide  has  entirely 
disappeared,  the  reaction  is  completed. 


198       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

N 
2.8  cc.  of  the  -  -  V.  S.  should  be  required,  each  cc. 

corresponding  to  0.5$  of  metallic  iron. 

The  reaction  between  the  ferric  nitrate  and  potas- 
sium iodide  is  as  follows: 

Fe2(N03),  +  2KI  -  2Fe(N03)2  +  2KNO3  +  I, 

2)483.1  2)253 

10)241.5  10)126.5 

24.i5gms.  12.65  gms. 

or  1000  cc.  —  V.  S. 
10 

Thus  each  cc.  of  the  decinormal  sodium  thiosulphate 
V.  S.  represents  0.02415  gm.  of  ferric  nitrate. 

Liquor  Ferri  Subsulphatis  (Solution  of  Basic  Ferric 
Sulphate;  Monsel's  Solution). — An  aqueous  solution  of 
basic  ferric  sulphate  of  variable  composition,  chemi- 
cally corresponding  to  about  13.6$  of  metallic  iron. 

1. 12  (i.i  I7)gms.  of  the  solution  are  introduced  into  a 
flask  (having  a  capacity  of  100  cc.),  together  with  15  cc. 
of  water  and  2  cc.  of  hydrochloric  acid.  I  gm.  of 
potassium  iodide  is  then  added  and  the  mixture 
digested  for  half  an  hour  at  a  temperature  of  40°  C. 
(104°  F.).  It  is  then  cooled,  and  after  adding  a  few 
drops  of  starch  T.  S.,  it  is  titrated  with  decinormal 
sodium  thiosulphate  V.  S.  When  the  blue  or  greenish 
color  of  the  liquid  disappears,  the  reaction  is  completed. 
27.2  cc.  should  be  required  to  complete  the  reaction, 
each  cc.  corresponding  to  0.5$  or  0.0056  gm.  of  metal- 
lic iron. 

0.0056  X  27.2  =  0.15232  gm. 

0.15232x100  6 

1. 12  *     ' 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       IQQ 

Liquor  Ferri  Tersulphatis  (Solution  of  Ferric  Sul- 
phate). —  An  aqueous  solution  of  normal  ferric  sulphate 


Fe2(SO4)3=  |  *'       containing  about  28.7  per  cent. 


of  the  salt,  and  corresponding  to  about  8  per  cent,  of 
metallic  iron. 

1.  12  (i.i  176)  gms.  of  the  solution  are  introduced  into 
a  loo-cc.  glass-stoppered  bottle,  together  with  15  cc.  of 
water  and  2  cc.  of  hydrochloric  acid  ;  I  gm.  of  potas- 
sium iodide  is  then  added,  and  the  mixture  kept  at  a 
temperature  of  40°  C  (104°  F.)  for  half  an  hour,  then 
allowed  to  cool,  and  the  liberated  iodine  estimated  in 

N 
the  usual  way  with  —  sodium  thiosulphate  V.  S.,  using 

starch  T.  S.  as  indicator. 

N 
About  16  cc.  of  the  —  V.  S.  should  be  required. 

The  following  equation  illustrates  the  reaction  : 
pe2(S04)3  +  2KI  =  2FeS04  +  K2SO4  +  I,. 

2)399-2  2)253 

Io)i99.6  10)126.5 

19.96  gms.  12.65  Sms-   or 

N 
the  equivalent  of  1000  cc.  of  —  thiosulphate  V.  S. 


Thus  each  cc.  represents  0.01996  gm.  of  ferric  sul- 
phate, which  corresponds  to  0.5  per  cent,  or  0.0056  gm. 
of  metallic  iron. 

If  16  cc.  are  used,  the  solution  of  ferric  sulphate  con- 
tains 0.01996  X  16  =  0.31936  gm. 


X  IPO  = 


1.  12 


200      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

of  pure  ferric  sulphate,   and 

0.0056  X  16  =  0.0896  gm., 
.0896  x  100  ' 

1. 12 

of  metallic  iron. 

Hydrogen  Peroxide,  H2Oa  =  j  J3.92.__The  iodo- 

metric  method,  which  originated  with  Kingzett,  is 
based  upon  the  fact  that  iodine  is  liberated  from  po- 
tassium iodide  by  hydrogen  peroxide,  in  the  presence 
of  sulphuric  acid,  and  that  this  liberation  of  iodine  is  in 
direct  proportion  to  the  available  oxygen  contained  in 
the  peroxide. 

Then  by  determining  the  amount  of  iodine  liberated, 
the  available  oxygen  is  readily  found. 

H202  +  H,S04  +  2KI  -  K2S04  +  2H.O  +  I, 

2)34  2),6  2)253 


17  =  I  available  O  =     ~  126.5 


This  shows  that  126.5  gms.  of  iodine  are  liberated  by 
17  gms.  of  absolute  peroxide,  which  are  equivalent  to 
8  gms.  of  available  oxygen. 

N 
Thus  1000  cc.  of  —  sodium  thiosulphate  V.  S.,  which 

absorb  and  consequently  represent  12.65  gms-  of  iodine, 
are  equivalent  to  1.7  gms.  of  H.^O2  or  0.8  gm.  of  avail- 
able oxygen. 

N 
Each  cc.  of  this  —  V.  S.,  then,  represents,  of  HaO2 

^0.0017  gm.,  of  available  oxygen  *o.ooo8  gm. 

The  coefficients  for  weight  of  H3O3  and  of  oxygen, 
it  is  seen,  are  identical  with  those  used  in  the  perman- 
ganate process.  Therefore  the  coefficient  for  volume  is 
also  the  same  in  this  method  as  in  the  other,  namely, 
0.5594. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.      2OI 


The  process  is  carried  out  as  follows  :  Take  2  or  3  cc. 
of  sulphuric  acid,  dilute  it  with  about  30  cc.  of  water, 
add  an  excess  of  potassium  iodide  (about  I  gm.),  and 
then  I  cc.  of  hydrogen  peroxide.  After  the  mixture  has 
been  allowed  to  stand  five  minutes  starch  T.  S.  is  added, 

N 
and  the  titration  with  —  sodium  thiosulphate  begun. 

Note  the  number  of  cc.  required  to  discharge  the 
blue  color,  and  multiply  this  number:  by  0.0017  gm.  to 
find  the  quantity,  by  weight,  of  H.,O2 ;  by  0.0008  gm.  to 
find  the  weight  of  available  oxygen  ;  by  0.5594  cc.  to 
find  the  volume  of  available  oxygen. 

If  18  cc.  are  required,  the  solution  is  of  0.5594  X  18= 
10.0683  volume  strength. 

0.0017  X  1 8  =  .0306  or  3.06$  H2O2. 
0.0008  X  1 8  =  .0144  or  1.44$  of  oxygen. 

With  this  method  the  author  has  always  obtained 
satisfactory  results.  The  lack  of  uniformity  in  the  re- 
action, which  is  frequently  reported,  is  doubtless  due 
to  the  use  of  insufficient  acid. 

TABLE  OF  SUBSTANCES,  ESTIMATED  BY  DECINORMAL  SODIUM  TRIO- 
SULPHATE  V.  S. 


Name. 

Formula. 

Molecular 
Weight. 

Factors. 

Chlorine            

Clo 

70.68 

Gm. 

Fe2(C2H3O2)« 

Ferric  chloride     

Fe2Cl6  +  i2H2O 

Feo<C«HRO,)Q 

488  48 

Ferric  nitrate  

Fe2(\O3)6 

483.1 

Ferric  phosphate   
Ferric  pyrophosphate  
Ferric  sulphate 

Fe2(PO4)2 
Fe4(P2O7i3  anhydrous 
Feo(SO4)3 

*302 

*746 

OI5I 

01865 

Ferric  and  ammonium  sulphate. 
Ferric  valerianate 

Fe2(NH4i2(S04)4+24H20 
Fe»(CtHuOo)« 

*  ;• 
*964.o 

*7i8 

0482 

Hydrogen  peroxide  

2H202 

33-92 

001606 

Iodine 

lo 

Iron,  in  ferric  salts   

Fe9 

i  n  .  76 

.005588 

Oxygen,  available,  weight  
Oxygen,  available  volume  ,. 

o/ 

02 

*32 

*32 

.0008 
•5594  cc- 

PART    II. 

CHAPTER  XIV. 
SANITARY  ANALYSIS  OF  WATER 

IN  collecting  samples  of  water  great  care  must  be 
exercised  in  order  to  secure  a  fair  representation  of 
the  water  and  to  avoid  the  introduction  of  foreign 
matters. 

The  samples  should  be  collected  in  clean  glass-stop- 
pered bottles  having  a  capacity  of  from  2  to  5  pints. 

It  is  well  to  completely  fill  the  bottle  with  water, 
then  empty  it,  and  again  fill  with  the  water  to  be  ana- 
lyzed. 

In  taking  samples  from  lakes,  reservoirs,  or  slow 
streams  the  bottle  should  be  submerged,  so  as  to  avoid 
collecting  any  water  that  has  been  in  direct  contact 
with  the  air. 

In  collecting  from  pump-wells  a  few  gallons  should 
be  pumped  out  before  taking  the  sample  in  order  to 
remove  that  which  has  been  standing  in  the  pump. 

If  the  public  water-supply  is  to  be  analyzed,  take  the 
water  from  a  hydrant  communicating  directly  with  the 
street  main,  and  not  from  a  cistern. 

At  the  time  of  collecting,  a  record  should  be  made  of 
those  surroundings  and  conditions  which  might  influ- 

202 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       203 

ence  the  character  of  the  water,  such  as  proximity  of 
cesspools,  sewers,  stables,  and  factories. 

It  should  also  be  noted  whether  the  sample  is  from  a 
deep  or  shallow  well,  a  river,  spring,  or  artesian  well. 

The  nature  of  the  soil  and  the  different  strata  of  the 
locality  must  also  be  taken  into  account. 

The  sample  should  be  kept  in  the  dark  and  analyzed 
with  as  little  delay  as  possible. 

Color. — This  may  be  taken  by  looking  down  through 
a  column  of  water  in  a  colorless  glass  tube  about  two 
feet  long,  standing  upon  a  piece  of  white  paper. 

A  comparison  is  made  with  a  second  tube  containing 
distilled  water. 

Another  way  of  determining  the  color  is  by  the  use 
of  a  colorless  glass  tube  two  feet  long  and  two  inches 
in  diameter,  closed  at  each  end,  with  disks  of  colorless 
glass  cemented  on,  but  having  a  small  opening  at  one 
end  for  filling  and  emptying  the  tube. 

To  use  this  tube,  it  is  half  filled  with  the  water  to  be 
examined  and  placed  in  a  horizontal  position.  A  piece 
of  white  paper  is  held  at  one  end  of  the  tube,  and  then 
by  looking  through  from  the  other  end  the  color  of  the 
liquid  is  observed,  and  a  comparison  of  tint  made  be- 
tween the  lower  half  of  the  tube  containing  the  water 
and  the  upper  half  containing  air. 

Odor. — Three  or  four  ounces  of  water  are  placed  in  a 
small  flask  fitted  with  a  cork  through  which  is  passed  a 
thermometer ;  the  flask  is  placed  in  a  water-bath  and 
heated  to  100°  F.  The  flask  is  then  shaken,  the  cork 
withdrawn,  and  the  odor  immediately  observed. 

In  this  way,  satisfactory  and  uniform  tests  are  ob- 
tained, and  a  practised  nose  can  frequently  detect 
pollution. 


204      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

Reaction. — This  may  be  determined  by  the  use  of  a 
neutral  solution  of  litmus.  If  an  acid  reaction  is  ob- 
tained, the  water  should  be  boiled  in  order  to  determine 
if  it  is  due  to  carbonic  acid ;  if  the  red  color  disappears 
upon  boiling,  the  acid  reaction  is  due  to  carbonic  acid. 

Phenolphthalein  or  lacmoid  may  also  be  used  for  this 
purpose. 

Suspended  Matter.— A  litre  of  the  turbid  water  is 
passed  through  a  dried  and  weighed  filter.  The  filter 
is  then  again  dried  and  weighed,  and  the  increase  in 
weight  represents  the  suspended  matter  in  one  litre  of 
the  water. 

TOTAL   SOLIDS. 

A  platinum  dish  having  a  capacity  of  about  120  cc, 
is  heated  to  redness,  then  cooled  under  a  desiccator, 
and  weighed.  100  cc.  of  the  water  is  then  intro- 
duced and  evaporated  over  a  low-temperature  burner 
at  a  moderate  heat.  When  the  residue  appears  dry 
the  heat  may  be  increased  by  placing  the  dish  in 
an  air  oven  kept  at  a  temperature  of  about  212°  F. 
until  it  ceases  to  lose  weight ;  finally  cool  under  a  desic- 
cator, and  weigh.  In  waters  of  exceptional  purity  it 
may  be  advisable  to  use  larger  quantities,  such  as  250  cc. 

The  increase  in  weight  of  the  dish  represents  approxi- 
mately the  total  solids  contained  in  the  water  taken. 

If  the  solid  residue  does  not  exceed  57  parts  per 
100,000,  no  reason  is  afforded  for  rejecting  the  water 
for  domestic  use.  It  has  been  found  that  the  figure 
for  total  solids  obtained  thus,  does  not  truly  represent 
the  sum  of  the  organic  and  mineral  matters  in  all 
cases. 

Experiments  have  been  made  with  urea  dissolved  in 


A   TEXT- BOOK    OF   VOLUMETRIC   ANALYSIS. 

varying  quantities  of  water.  Where  the  solution  con- 
tained i  gm.  of  urea  the  residue  after  evaporation 
varied  from  0.98  to  0.007  §m* 

Besides  the  possible  loss  of  organic  matter  during 
the  evaporation,  some  of  the  mineral  constituents  may 
retain  with  great  obstinacy,  large  quantities  of  water  in 
the  form  of  water  of  crystallization,  which  would  cause 
an  error  in  the  opposite  direction. 

Thus  the  determination  of  total  solids  is  only  an  ap- 
proximation. 

ORGANIC  AND  VOLATILE  MATTER — LOSS  ON  IGNITION. 

Though  the  mineral  matter  in  a  water  must  to  some 
extent  be  taken  into  account  in  judging  of  a  water, 
the  organic  matter  is  of  far  greater  importance.  The 
really  injurious  matters  are  more  probably  the  organic. 

It  is  therefore  important  to  determine  as  near  as 
possible  their  quantity  and  nature. 

It  was  naturally  supposed  that  by  igniting  the  resi- 
due obtained  from  evaporation  of  the  water,  the  or- 
ganic matter  would  be  burned  out,  and  that  the  loss 
of  weight  would  then  represent  the  organic  matter. 
But  as  waters  ordinarily  contain  some  earthy  carbo- 
nates, which  upon  ignition  are  deprived  of  carbonic-acid 
gas  and  converted  into  oxides,  it  was  customary  to  add 
a  few  drops  of  carbonic-acid  water  or  ammonium  car- 
bonate to  the  ash,  and  then  dry  and  weigh  the  residue. 

Ignition,  however,  decomposes  other  salts  which  may 
be  contained  in  water,  and  may  even  volatilize  some 
wholly ;  therefore  the  loss  on  ignition  cannot  be  truly 
called  the  organic  matter.  Hence  the  expressions  "  Or- 
ganic and  Volatile  Matter,"  and  "  Loss  on  Ignition." 

Frankland  recommends  ignition  as  a  rough  qualita- 


2O6       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

tive  test  for  the  presence  of  organic  matter,  the  degree 
of  blackening  which  takes  place,  giving  some  idea  of 
the  probable  amounts  of  organic  matter  present. 

CHLORINE 

may  be  estimated  by  the  use  of  decinormal  or  centi- 
normal  silver-nitrate  solution ;  but  analysts  generally 
use  a  solution  of  such  strength  that  I  cc.  will  represent 
o.ooi  gm.  of  chlorine. 

Standard  Silver-nitrate  Solution.  —  Dissolve  4.794 
gms.  of  pure  recrystallized  silver  nitrate  in  sufficient 
water  to  make  1000  cc. 

Potassium-chr  ornate  Solution. — Five  gms.  of  neutral 
potassium  chromate  are  dissolved  in  100  cc.  of  water 
and  a  weak  solution  of  silver  nitrate  added,  drop  by 
drop,  until  a  slight  permanent  red  precipitate  is  pro- 
duced, which  is  allowed  to  settle  in  the  bottle,  or  sepa- 
rated by  filtration. 

The  Process. — Measure  out  100  cc.  of  the  water  to 
be  analyzed  into  a  beaker  or  white  basin  ;  add  a  few 
drops  of  the  potassium-chromate  solution  ;  then  run  in 
slowly  from  a  burette,  the  silver-nitrate  solution  until 
a  slight  red  tint  appears.  Note  the  number  of  cc.  of 
silver  solution  used.  Each  cc.  represents  o.ooi  gm. 
(i  milligramme).  If  the  chlorine  is  present  in  small 
quantity,  about  250  cc.  of  the  water  should  be  evapo- 
rated to  about  one  fifth  before  titrating  with  the 
silver-nitrate  solution. 

Example. — 100  cc.  of  water  taken,  4  cc.  of  silver 
solution  consumed  ;  thus  showing  that  the  100  cc.  of 
water  contained  0.004  gm-  °*  chlorine,  or  100,000  cc. 
contained  4  gms. 

Multiplied  by  10  gives  parts  per  million. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.      2O/ 

The  water  must  be  perfectly  neutral  before  titration. 
If  acid,  it  must  be  shaken  with  a  little  pure  precipi- 
tated calcium  carbonate. 

AMMONIA. 

When  organic  matter  decomposes  spontaneously,  it 
first  forms  ammonia,  then  nitrites,  and  finally  nitrates. 
Thus  the  presence  of  ammonia  in  water  is  generally 
conceded  to  indicate  decomposing  organic  matter,  and 
hence  its  determination  is  an  important  part  of  the 
sanitary  examination  of  water. 

The  ammonia  is  generally  spoken  of  as  free  am- 
monia and  albuminoid  ammonia,  or,  more  properly,  as 
ammonium  salts  and  ammonia  from  organic  nitrogen. 

The  sanitary  examination  of  a  water  should  always 
include  a  quantitative  determination  of  nitrogen  in 
both  compounds. 

The  process  requires  several  solutions  and  consider- 
able care  in  manipulation.  The  solutions  required  are  : 

I.  Nesslers  Solution,  made  by  dissolving  35  gms.  of 
potassium  iodide  in  100  cc.  of  water  and  17  gms.  of 
mercuric  chloride  in  300  cc.  of  water.  The  liquids 
may  be  heated  to  aid  solution,  but  if  so,  must  be  again 
cooled.  When  solution  is  complete,  add  the  latter 
to  the  former  until  a  permanent  precipitate  is  pro- 
duced ;  then  dilute  with  a  20$  solution  of  sodium 
hydroxide  to  1000  cc.  Now  add  mercuric-chloride 
solution  again  until  a  permanent  precipitate  is  formed. 
Let  the  mixture  stand  until  settled,  then  decant  off 
the  clear  solution  for  use.  The  bulk  of  the  solution 
should  be  kept  in  a  well-stoppered  bottle,  and  a  small 
quantity  transferred  from  time  to  time  to  a  small 
bottle,  from  which  it  should  be  used.  This  solution 


208      A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

improves  on  keeping,  and  reacts  with  extremely  min- 
ute quantities  of  ammonia. 

2.  Sodium-carbonate    Solution.  —  A    20$   solution    of 
pure    freshly-ignited    sodium   carbonate   in  water  free 
from  ammonia. 

3.  Standard  Ammonium-chloride  Solution. — Dissolve 
0.3138  (^.314)  gm.  of  pure  ammonium  chloride  in  water 
to  100  cc.     For  use  dilute  I  cc.  of  this  solution  with  99 
cc.  of  distilled  water  free  from  ammonia.     Each  cc.  of 
this  solution  contains  o.ooooi  gm.  of  ammonia. 

4.  Alkaline   Potassium-permanganate  Solution. — Dis- 
solve 200  gms.  of  pure  potassium  hydroxide  and  8  gms. 
of  pure  potassium  permanganate  in  sufficient  ammonia- 
free  water  to  make  1000  cc. 

5.  Ammonia-free    Water. — If   the  distilled   water   of 
the  laboratory  gives  a  reaction  with  Nessler's  solution, 
it  should  be   treated  with  sodium  carbonate,  about   I 
gm.  to  the  litre,  and  boiled  until  one  fourth  has  been 
evaporated. 

A  good  clear  hydrant  water  when  treated  with  so- 
dium carbonate  and  distilled  yields  ammonia-free  water. 
The  first  portion  which  comes  over  has  of  course 
some  ammonia  in  it,  and  small  portions  of  the  distil- 
late should  be  tested  with  Nessler's  reagent  until  no 
more  reaction  is  obtained  ;  the  remainder,  except  the 
very  last  portion,  should  be  collected. 

Ammonia-free  water  may  also  be  obtained  by  distil- 
ling water  acidulated  with  sulphuric  acid.  In  the  first 
two  processes  the  ammonia  is  converted  into  a  volatile 
salt  and  is  easily  dissipated,  or  appears  in  the  first  distil- 
late ;  in  the  last  process  it  is  converted  into  a  non-vol- 
atile salt,  which  does  not  distil  over. 

Apparatus  Required. — A  still,  consisting  of  a  glass 


A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.      2OQ 

retort,  having  a  capacity  of  about  700  cc.,  which  is  con- 
nected with  a  Liebig's  condenser  by  an  air-tight  joint. 
The  heat  is  applied  by  means  of  a  low-temperature 
burner,  the  iron  ring  of  which  is  removed,  so  that  the 
retort  rests  directly  upon  the  gauze.  (See  Fig.  25.) 


FIG.  25. 

Cylinders  for  Comparative-color  Tests. — These  cylin- 
ders are  made  of  pure  colorless  glass,  about  one  inch 
in  diameter,  having  a  capacity  of  about  100  cc.  and 
graduated  at  50  cc.  These  should  either  have  a  milk- 
glass  foot,  or  should  stand  upon  white  paper.  Two  or 
more  of  these  are  required. 


210      A  TEXT-BOOK   OF  VOLUMETRIC   ANALVSIS. 

The  Process. — The  retort  and  condenser  are  thor- 
oughly rinsed  out  with  ammonia-free  water.  Then  500 
cc.  of  the  water  to  be  tested  are  introduced,  and  about 
5  cc.  of  sodium-carbonate  solution  added  to  make  the 
water  alkaline.  The  water  is  then  gently  boiled  until 
50  cc.  of  distillate  are  obtained.  This  distillate  is 
transferred  to  one  of  the  color-comparison  cylinders 
and  2  cc.  of  Nessler's  reagent  added  ;  a  yellow  color  is 
produced,  which  develops  more  fully  in  3  or  5  minutes, 
and  the  intensity  of  which  is  proportionate  to  the 
amount  of  ammonia  present. 

The  color  produced  is  exactly  matched  by  introduc- 
ing into  another  cylinder  50  cc.  of  ammonia-free  water 
and  an  accurately  measured  quantity  of  the  standard 
ammonium-chloride  solution,  and  2  cc.  of  Nessler's 
reagent,  as  before. 

According  as  the  color  so  produced  is  deeper  or 
lighter  than  that  obtained  from  the  water,  other  solu- 
tions are  prepared  for  comparison,  containing  smaller 
or  larger  proportions  of  the  ammonium  chloride,  until 
the  proper  color  is  produced. 

The  distillation  is  continued,  and  successive  portions 
of  50  cc.  of  the  distillate  taken  and  tested,  until  the 
liquid  no  longer  reacts  with  Nessler's  reagent.  The. 
sum  of  the  figures  obtained  from  the  several  distillates 
gives  the  total  ammonia,  existing  in  ammonium  com- 
pounds, in  the  500  cc.  of  water  taken. 

The  residue  in  the  retort  serves  for  the  determina- 
tion of  the  nitrogen  of  the  organic  matter,  which  is 
converted  by  the  alkaline  permanganate  into  ammonia 
(albuminoid  ammonia). 

50  cc.  of  the  alkaline  permanganate  are  placed  in  a 
porcelain  dish  of  about  150  cc.  capacity,  the  dish  nearly 


A   TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       211 

filled  with  distilled  water,  and  then  the  liquid  boiled 
down  to  50  cc. 

This  is  added  to  the  residue  in  the  retort,  the  distil- 
lation resumed,  and  the  ammonia  estimated  in  each 
50  cc.  of  the  distillate,  as  before  described. 

It  is  the  practice  of  some  analysts  to  mix  the  distil- 
lates of  each  of  the  above  operations,  and  thus  make 
determinations  merely  of  the  total  quantity  of  ammo- 
nia and  albuminoid  ammonia.  By  so  doing  valuable 
information  may  be  lost,  since  it  has  been  pointed  out 
that  the  ammonia  may  be  differently  distributed  in 
the  distillates,  according  to  the  state,  decomposing  or 
otherwise,  in  which  the  ammonia  exists  in  the  water. 
If  the  ammonia  distils  over  very  rapidly,  it  indicates 
that  the  organic  matter  is  in  a  putrescent  or  decom- 
posing condition. 

If,  on  the  other  hand,  it  distils  gradually,  it  indicates 
the  presence  of  organic  matter  in  a  comparatively  stable 
or  fresh  condition.  It  is  best,  therefore,  to  keep  the 
record  of  each  distillate,  so  that  the  rapidity  with 
which  the  ammonia  is  set  free,  as  well  as  the  actual 
amount,  may  be  known. 

The  greatest  care  should  be  exercised  in  order  to 
avoid  the  introduction  of  ammonia  in  any  way  during 
the  course  of  the  analysis,  since  small  quantities  of 
ammonia  compounds  and  nitrogenous  matters  are 
everywhere  present.  All  measuring-vessels,  cylinders, 
etc.,  should  be  thoroughly  rinsed  before  using. 

NITROGEN  AS   NITRATES. 

Solutions  Required. — Acid  Phenyl  Sulphate. — 18.5 
cc.  of  strong  sulphuric  acid  are  added  to  1.5  cc.  of 


212       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

water  and  3  gms.  of  pure  phenol.  This  should  be  pre- 
served in  a  tightly-stoppered  bottle. 

Standard  Potassium  Nitrate. — 0.722  gm.  of  pure 
potassium  nitrate,  previously  heated  to  a  temperature 
just  sufficient  to  fuse  it,  is  dissolved  in  water,  and  the 
solution  made  up  to  1000  cc.  I  cc.  of  this  solution 
will  contain  .0001  gm.  of  nitrogen. 

The  Process. — A  measured  volume  of  water  is  evap- 
orated just  to  dryness  in  a  platinum  or  porcelain  dish, 
I  cc.  of  the  acid  phenyl  sulphate  added  and  thoroughly 
mixed  with  the  residue  by  means  of  a  glass  rod,  then 
I  cc.  of  water  and  three  drops  of  strong  sulphuric  acid, 
and  the  dish  gently  warmed.  ,The  liquid  is  then 
diluted  with  about  25  cc.  of  water,  a  slight  excess  of 
ammonium  hydroxide  added,  and  the  solution  made 
up  to  100  cc. 

The  reactions  are : 

HC6HBS04+3HN03=HC6H2(N02)30+H2S04+2HaO 

Acid  phenyl  Trinitrophenol 

sulphate.  (picric  acid). 

HC6H2(NO2)3O  +NH4OH  ==  NH4C6H2(NO2)3O-L-  H2O. 

Ammonium  picrate. 

The  nitric  acid  used  in  the  above  equation  is  derived 
from  the  potassium  nitrate  by  the  action  of  sulphuric 
acid. 

The  ammonium  picrate  imparts  a  yellow  color  to 
the  solution,  the  intenstiy  of  which  is  proportional  to 
the  amount  present. 

Five  cc.  of  the  standard  potassium-nitrate  solution  are 
now  similarly  evaporated  in  a  platinum  basin,  treated 
as  above,  and  made  up  to  100  cc.  The  color  produced 


A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.       213 

is  compared  to  that  given  by  the  water ;  and  one  or 
the  other  of  the  two  solutions  diluted  until  the  tints 
agree. 

The  comparative  volumes  of  the  liquids  furnish  the 
necessary  data  for  determining  the  amount  of  nitrate 
present,  as  the  following  example  will  show.  Five 
cc.  of  the  standard  nitrate  are  treated  as  above,  and 
made  up  to  100  cc.  Each  cc.  represents  o.oooi  gm.  of 
nitrogen. 


.0005  gm.  N  per  100  cc. 


.0050  gm.  N  per  1000  cc. 

Suppose  100  cc.  of  water  similarly  treated  are  found 
to  require  dilution  to  I5occ.  before  the  tint  will  match 
that  of  the  standard  ;  then 

IOO  :  150  ::  .005  :  x.      x  =  0.0075. 

That  is,  the  water  contains  7.5  milligrams  of  nitrogen 
as  nitrate  per  litre. 

Care  should  be  taken  that  the  same  quantity  of  acid 
phenyl  sulphate  is  used  for  the  water  and  for  the  com- 
parison liquid,  otherwise  different  tints  instead  of  depths 
of  tints  are  produced. 

With  river  or  spring  waters  25  to  IOO  cc.  should  be 
evaporated  for  the  test,  but  with  subsoil  and  other 
waters  which  probably  contain  much  nitrates  10  cc. 
will  be  sufficient. 


214      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

The  Copper-zinc  Process. — 500  cc.  of  the  water  are 
acidulated  with  oxalic  acid,  and  half  of  this  is  poured 
into  each  of  two  wide-mouthed  bottles.  Into  one  of 
these  is  put  a  copper-zinc  couple,  made  by  taking  a 
piece  of  sheet  zinc  (4X6  in.)  and  rolling  it  into  a  loose 
coil  and  immersing  it  in  a  i.5-per-cent.  solution  of 
copper  sulphate  until  the  surface  is  covered  with  an 
even  layer  of  copper. 

Cork  both  bottles  and  let  stand  24  hours.  Remove 
50  cc.  from  each  bottle  and  Nesslerize  as  directed  under 
Ammonia. 

The  difference  between  the  two  readings  gives  the 
ammonia  due  to  the  reduction  of  the  nitrates  and 
nitrites  present.  The  nitrogen  in  the  nitrites,  which  is 
separately  determined,  must  be  subtracted,  when  the 
remaining  nitrogen  will  be  that  from  the  nitrates. 


NITROGEN   AS  NITRITES. 

Solutions  Required. — i.  Naphthylammonium  Chlo- 
ride (Naplithalamin  HydrocJilorate). — Saturated  solu- 
tion in  water  free  from  nitrites.  It  should  be  colorless 
(0.5  gm.  dissolved  in  100  cc.  of  boiling  water).  This 
solution  should  be  kept  in  a  glass-stoppered  bottle  with 
a  little  animal  charcoal,  which  will  keep  the  solution 
colorless, 

2.  Sulphanilic  Acid  (Para-amido-benzene — Sulphonic 
Acid). — A  saturated  solution  in  water  free  from  nitrites 
(i  gm.  in  100  cc.  of  hot  water). 

Hydrochloric  Acid. — 25  cc.  of  concentrated  pure  hy- 
drochloric acid  mixed  with  75  cc.  of  water  free  from 
nitrites. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

Standard  Sodium  Nitrite.  —  0.275  gm.  pure  silver 
nitrite  is  dissolved  in  pure  water,  and  a  dilute  solution 
of  pure  sodium  chloride  added  until  a  precipitate  ceases 
to  form.  It  is  then  diluted  with  pure  water  to  250  cc. 
and  allowed  to  stand  until  clear.  For  use  10  cc.  of 
this  solution  are  diluted  to  100  cc.  It  must  be  kept 
dark.  One  cc.  of  the  dilute  solution  is  equivalent  to 
.00001  gm.  of  nitrogen. 

A  standard  solution  of  silver  nitrite  is  used  by  some 
chemists,  but  the  above  is  said  to  give  better  results. 

The  Process. — 100  cc.  of  the  water  is  placed  in  one 
of  the  color-comparison  cylinders,  the  measuring-vessels 
and  cylinder  having  previously  been  rinsed  with  the 
water  to  be  tested.  By  means  of  a  pipette  introduce 
into  the  water  i  cc.  each  of  the  solutions  of  sulphanilic 
acid,  dilute  hydrochloric  acid,  and  naphthylammonium- 
chloride  solution  in  the  order  named.  It  is  convenient 
to  have  three  pipettes — one  for  each  of  these  solutions, 
and  to  use  them  for  no  other  purpose.  In  all  cases  the 
pipettes  should  be  rinsed  with  ammonia-free  water 
before  using  them.  Into  another  clean  comparison- 
cylinder  introduce  I  cc.  of  the  standard  nitrite  solution 
and  make  up  to  100  cc.  with  pure  water ;  then  add  the 
same  reagents  as  were  added  to  the  water  in  the  other 
cylinder. 

A  pink  color  is  produced  in  the  presence  of  nitrites, 
which  requires  in  dilute  solutions  half  an  hour  for  com- 
plete development.  At  the  end  of  that  time  the  darker 
solution  is  diluted  with  water  until  the  tints  are 
matched,  and  the  calculation  made  as  explained  under 
nitrates. 

The  reactions  are  explained  by  the  following  equa- 
tions : 


2l6      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

CaH4NH,HSO§  +  HN02  =  C6H4N2SO3  +  2H8O; 

Sulphanilic  acid.  Para-diazo-benzene-sulphonic  acid. 


C.H«N,SO,  +  C10H7NH3C1 

ithammoniur 
chloride. 

=  Ct.H6(NHi)NNC.H4HSOi  +  HC1. 


Naphthammonium 
chloride. 


Azo-alpha-amido-naphthalene- 
parazo-benzene-sulphonic  acid. 

The  last-named  body  gives  the  color  to  the  liquid. 

Example. — Suppose  that  100  cc.  of  the  water  re- 
quire dilution  to  125  cc.  in  order  to  bring  it  to  the 
same  tint  as  that  produced  by  I  cc.  of  the  standard 
nitrite  solution,  which  contains  .0000 1  gm.  of  nitrogen 
as  nitrite. 

100  :  125  ::  .00001  :  x.    0.0000125  gm.  in  100. 

That  is,  100  cc.  of  water  contain  0.0000125  gm.  of  N  ; 
0.0125  gm.  in  100,000  cc. 

OXYGEN-CONSUMING  POWER. 

Potassium  permanganate  readily  yields  up  ics  oxy- 
gen, especially  in  the  presence  of  a  strong  mineral  acid, 
as  sulphuric.  It  oxidizes  many  salts,  and  organic  mat- 
ter. 

This  property  led  to  the  idea  that  this  salt  may  be 
used  for  burning  up  (chemically  speaking)  the  organic 
matter  in  water,  and  that  the  quantity  of  permanganate 
used  could  be  relied  upon  as  a  means  of  measuring  the 
organic  matter  in  water. 

This  method  does  not  distinguish  between  ani- 
mal and  vegetable  matter,  nor  does  the  quantity  of 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

permanganate  consumed  represent  only  the  organic 
matter. 

The  organic  matters  in  water  are  very  variable  in 
character  and  condition,  and  their  oxidability  is  subject 
to  much  difference. 

Nevertheless  as  a  high  oxygen-consuming  power 
certainly  indicates  pollution  by  organic  matter,  the 
process  is  of  considerable  value. 

The  following  is  a  convenient  method  for  approxi- 
mating the  oxygen-consuming  power  of  a  water: 

Solutions  Required. — Potassium  Permanganate. — 
0.395  gm.  of  pure  potassium  permanganate  is  dissolved 
in  distilled  water,  and  the  solution  made  up  to  looocc. 
i  cc.  of  this  solution  will  yield  under  favorable  circum- 
stances o.oooi  gm.  of  oxygen. 

Diluted  Sulpliuric  Acid. — 50  cc.  of  pure  sulphuric  acid 
are  mixed  with  100  cc.  of  water,  and  then  just  sufficient 
of  the  permanganate  solution  added  to  give  the  mixture 
a  faint  pink  color,  which  remains  after  standing  in  a 
warm  place  four  hours. 

The  Process. — Five  stoppered  bottles  having  a  capac- 
ity of  500  cc.  are  thoroughly  cleansed  with  strong  sul- 
phuric acid  and  then  carefully  rinsed  with  pure  water, 
and  250  cc.  of  the  water  to  be  tested  put  into  each  one. 
10  cc.  of  the  dilute  sulphuric  acid  is  then  added  to 
each,  together  with  regularly  increasing  quantities  of  the 
standard  permanganate,  say  2,  4,  6,  8,  and  iocc.,  respec- 
tively. 

At  the  end  of  an  hour  they  should  be  examined,  to 
see  which,  if  any,  are  decolorized.  At  the  end  of  the 
fourth  hour  they  should  again  be  examined,  and  again 
at  the  expiration  of  twenty-four  hours. 

If  all  of  the  bottles  are  decolorized  at  or  before  the 


218      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

fourth  hour  an  additional  10  cc.  of  the  permanganate 
solution  should  be  added  to  each  bottle. 

With  ordinary  waters  the  first  and  probably  the 
second  bottle  will  be  decolorized,  while  a  little  color 
will  remain  in  the  third,  and  the  color  in  the  fourth  and 
fifth  will  be  but  little  diminished.  In  this  way  an  ap- 
proximate figure  for  the  oxygen-consuming  power  of 
the  water  may  be  obtained,  which  in  most  cases  is  all 
that  is  necessary.  If  a  closer  figure  is  desired,  the  ex- 
periment may  be  repeated,  using  quantities  of  perman- 
ganate intermediate  between  those  marking  the  limits 
of  the  reaction. 

Thus  if  the  second  bottle  is  decolorized  and  a  faint 
color  still  remains  in  the  third,  repeat  the  experiment 
with  5  cc.  of  the  permanganate. 

This  method  of  procedure  has  an  advantage  over 
some  of  the  other  processes,  because  the  rate  of  oxida- 
tion can  easily  be  seen.  This  is  considered  by  some  to 
be  of  more  importance  than  the  actual  amount  of  oxy- 
gen consumed. 

It  must  be  remembered  that  nitrites,  ferrous  salts, 
sulphides,  etc.,  consume  oxygen  as  well  as  organic  mat- 
ter. It  is  therefore  important  to  boil  water  containing 
hydrogen  sulphide  in  order  to  drive  the  latter  off. 
Nitrites  may  be  removed  by  treating  the  water  with 
sulphuric  acid,  and  boiling.  The  nitrite  is  thus  con- 
verted into  nitrous  acid,  which  is  driven  off  by  the  heat. 
Or  the  oxygen  required  to  convert  the  nitrites  pres- 
ent into  nitrates  may  be  deducted  from  the  total 
amount  of  oxygen  consumed.  14  parts  of  nitrogen  as 
nitrite  require  16  parts  of  oxygen  for  oxidation  into 
nitrate. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       2IQ 
PHOSPHATES. 

Solutions  Required. — Ammonium  Molybdate. — Made 
by  dissolving  10  gms.  of  molybdic  anhydride  in  a  mix- 
ture of  15  cc.  of  concentrated  ammonia  (sp.  gr.  .900)  and 
25  cc.  of  water.  This  solution  is  poured  slowly,  and  with 
constant  stirring,  into  a  mixture  of  65  cc.  of  concen- 
trated nitric  acid  (sp.  gr.  1.4)  and  65  cc.  of  water,  and 
allowed  to  stand  until  clear.  It  should  be  kept  dark. 

The  Process. — One  litre  of  the  water  is  evaporated 
to  about  50  cc.;  a  few  drops  of  a  dilute  solution  of  ferric 
chloride  are  added,  followed  by  a  slight  excess  of  am- 
monia. Ferric  hydroxide  is  thus  precipitated,  which 
carries  down  with  it  all  the  phosphate.  This  precipi- 
tate is  separated  by  filtration,  dissolved  on  the  filter 
in  the  smallest  possible  quantity  of  hot  dilute  nitric 
acid,  and  a  little  water  passed  through  the  filter.  The 
filtrate  and  washings  should  not  exceed  5  cc.,  and 
should,  if  more,  be  evaporated  to  this  bulk. 

The  solution  is  now  heated  nearly  to  boiling  and  2 
cc.  of  the  ammonium-molybdate  solution  added.  If 
after  half  an  hour  an  appreciable  precipitate  is  formed, 
it  is  collected  on  a  small  weighed  filter  and  its  weight 
found  after  thorough  drying.  This  weight,  multiplied 
by  0.05  gives  the  amount  of  PO4.  If  the  quantity  is  too 
small  to  be  collected  and  weighed  in  this  manner,  it  is 
usually  reported  as  "  traces,"  "  heavy  traces,"  or  "  very 
heavy  traces." 

HARDNESS. 

The  hardness  of  water,  that  is,  its  soap-destroying 
power,  is  due  principally  to  the  presence  of  calcium 
salts ;  but  salts  of  magnesium,  iron,  and  other  metals 
may  also  contribute  to  this  effect. 


220      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

Two  kinds  of  hardness  are  recognized : 

1.  "Temporary,"  which   is  due  to   the  presence  in 
water  of  the  acid   carbonates  of  calcium,  magnesium, 
etc.     By  boiling,  these  salts  are  decomposed,  the  car- 
bonic-acid gas  being  driven  off,  and  the  neutral  carbon- 
ate formed,   which    is   precipitated.     Thus   the  water 
loses  its  hardness  upon  boiling. 

CaH2(CO3)2  =  CaC03  +  HaO  +  COa. 

2.  "  Permanent  "  hardness  is  due  to  the  presence  in 
water  of  salts  of  the  above-mentioned  metals  which 
are  not  removed  by  boiling,  such  as  the  sulphates. 

Hardness  is  estimated  by  means  of  a  standard  soap 
solution. 

Many  samples  of  water  possess  both  temporary  and 
permanent  hardness,  and  it  is  sometimes  desirable  to 
estimate  them  separately. 

The  total  hardness  is  estimated  in  one  sample,  and 
the  hardness  in  another  sample  is  determined  after 
boiling  and  filtering  off  the  precipitated  calcium  car- 
bonate. 

The  hardness  found  after  boiling  is  the  permanent 
hardness,  and  is  the  most  objectionable  form.  The 
difference  between  the  total  and  permanent  hardness 
is  the  temporary  hardness.  To  express  the  hardness 
in  some  tangible  form,  the  usual  custom  in  this  coun- 
try and  in  England  is  to  give  results  in  the  correspond- 
ing amounts  of  calcium  carbonate,  i.e.,  practically  to 
determine  the  amount  of  soap  destroyed  by  a  meas- 
ured quantity  of  water,  and  then  to  state  the  results 
as  the  amount  of  calcium  carbonate  which  would  de- 
stroy that  quantity  of  soap. 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       221 

The  reaction  which  takes  place  when  soap  is  added 
to  a  hard  water,  is  illustrated  in  the  following  equa- 
tions : 

CaH,(COs),  +  2NaC,.H,.0, 

Acid  calcium          Sodium  stearate 
carbonate.  (Soap). 

=  Ca(C18H,A),  +  Na,CO,  +  H,O  +  CO, ; 

Calcium  stearate. 
or, 

CaS04  +  2NaC18H8A  =  Ca(C18H3602),  +  Na,SO, 

Calcium  sulphate. 

The  calcium  stearate,  which  is  an  insoluble  calcium 
soap,  is  precipitated  in  both  cases  as  a  white  curd-like 
mass. 

The  method  for  estimating  hardness  in  water  by  the 
use  of  soap  solution  is  known  as  Clark's  method. 

Solutions  Required. — Standard  Soap  Solution. — 
Dissolve  10  gms.  of  shavings  of  air-dried  Castile  soap 
in  a  litre  of  dilute  alcohol.  Filter  the  solution  if  it  is 
not  clear,  and  keep  it  in  a  tightly-stoppered  bottle. 

Standard  Calcium  Chloride  Solution. — Dissolve  I  gm. 
of  pure  calcium  carbonate  in  the  smallest  excess  of 
hydrochloric  acid,  then  carefully  neutralize  with  am- 
monia water,  and  add  sufficient  water  to  make  up  to 
one  litre. 

One  cc.  of  this  solution  will  contain  the  equivalent  of 
O.OOi  gm.  of  calcium  carbonate.  This  solution  is  used 
for  determining  the  strength  of  the  soap  solution, 
which  is  done  as  follows : 

Measure  out  10  cc.  of  this  solution,  add  90  cc.  of  dis- 
tilled water,  and  run  in  the  soap  solution,  drop  by  drop, 
from  a  burette  until  a  lather  is  formed,  which  remains 


222       A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

for  five  minutes.  Note  the  number  of  cc.  of  soap  so- 
lution used. 

We  now  repeat  the  experiment  with  100  cc.  of  dis- 
tilled water.  The  amount  of  the  soap  solution  re- 
quired to  produce  a  permanent  lather  with  the  distilled 
water  must  be  deducted  from  the  amount  used  in  the 
first  test.  Usually  it  will  be  about  one  half  or  one  cc. 

The  10  cc.  of  the  calcium  chloride  solution  contained 
the  equivalent  of  o.oio  gm.  of  CaCO3.  Suppose  in  the 
above-mentioned  test  8.5  cc.  of  the  soap  solution  were 
used  to  produce  a  permanent  lather,  and  0.5  cc.  were 
used  by  the  distilled  water.  Then  8  cc.  were  used  to 
precipitate  o.oio  gm.  of  CaCO3.  Thus  each  cc.  of  this 
soap  solution  will  represent  J  of  .010  gm.  —  .00125  of 
calcium  carbonate. 

The  soap  solution  may  either  be  used  as  it  is,  or  it 
may  be  diluted  with  dilute  alcohol  so  that  about  10.5 
or  1 1  cc.  of  it  will  be  required  to  produce  a  permanent 
lather  with  10  cc.  of  the  standard  calcium  chloride  so- 
lution. If  so  diluted  each  cc.  will  represent  o.ooi  gm. 
of  CaCO3. 

This  is  a  convenient  strength,  because  if  100  cc.  of 
water  are  operated  upon,  each  cc.  of  the  soap  solution 
used  will  represent  I  part  of  CaCO3  in  100,000  parts 
of  water. 

Measure  100  cc.  of  the  water  into  a  well-stoppered 
bottle  having  a  capacity  of  about  250  or  300  cc.  Add 
the  soap  solution  gradually  from  a  burette,  one  cc.  at 
a  time  at  first,  and  smaller  quantities  towards  the  end 
of  the  operation,  shaking  well  after  each  addition 
until  a  soft  lather  is  obtained,  which  if  the  bottle  is 
placed  at  rest  on  its  side,  remains  continuous  over  the 
whole  surface  for  five  minutes. 


A   TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       223 

The  soap  should  not  be  added  in  large  quantities  at 
a  time,  even  if  the  volume  required  is  approximately 
known. 

If  magnesium  salts  are  present,  a  kind  of  scum 
(simulating  a  lather)  will  be  seen  before  the  reaction  is 
completed.  The  character  of  this  scum  must  be  care- 
fully watched,  and  the  soap  solution  added  very  care- 
fully, with  an  increased  amount  of  shaking  after  each 
addition.  The  point  when  the  false  lather  due  to  the 
magnesium  salt  ceases  and  the  true  persistent  lather 
is  produced  is  comparatively  easy  to  distinguish. 

If  more  than  23  cc.  of  the  soap  solution  are  con- 
sumed by  the  100  cc.  of  water,  a  smaller  quantity  of 
water  should  be  taken  (say  50  or  25  cc.)  and  made  up 
to  100  cc.  with  distilled  water,  recently  boiled.  In 
such  case  the  quantity  of  soap  solution  used  must  be 
multiplied  by  2  or  4. 

If  the  first-mentioned  soap  solution  is  used  each  cc. 
represents  0.00125  gm.  If  the  second  solution  is  used 
each  cc.  represents  o.ooi  gm.  of  CaCO3,  and  if  100  cc. 
of  water  are  acted  upon  each  cc.  represents  I  part  of 
CaCO,  in  100,000. 

If  70  cc.  of  water  are  acted  upon,  instead  of  100  cc., 
each  cc.  of  soap  solution  used  represents  i  gm.  per 
70,000  cc.,  which  corresponds  to  I  gr.  per  imperial 
gallon  (70,000  grs.)  or  i  degree  of  hardness. 

These  estimations  are,  however,  only  approximate, 
for  the  lather  does  not  form  until  the  reaction  between 
the  soap  and  the  calcium  in  the  water  is  completed, 
and  then  the  quantity  of  soap  solution  required  to 
produce  the  lather  depends  upon  its  strength. 

Dr.  Clark,  the  originator  of  this  method,  has  shown 
that  1000  grains  of  distilled  water  (free  from  hardness) 


224       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

require  1.4  measures  of  soap  solution,  each  measure 
being  the  volume  of  10  grains  of  distilled  water  at  16°  C. 

For  Permanent  Hardness. — To  determine  the  hard- 
ness after  boiling,  a  measured  quantity  of  water  must  be 
boiled  briskly  for  half  an  hour,  adding  distilled  water 
from  time  to  time  to  make  up  the  loss  by  evaporation. 
At  the  end  of  the  half-hour  allow  the  water  to  cool, 
make  up  to  its  original  volume  with  recently  boiled  and 
cooled  distilled  water,  filter  rapidly,  and  test  in  the  same 
manner  as  described  above.  One  half  or  one  cc.  is  de- 
ducted from  the  soap  solution  used,  for  the  calculation. 

Among  German  chemists  it  is  customary  to  desig- 
nate the  soap-destroying  power  equivalent  to  I  part  of 
CaO  in  100,000,  as  one  degree  of  hardness. 

Among  French  chemists  each  degree  of  hardness 
represents  I  part  of  CaCO3  in  100,000. 

INTERPRETATION   OF   RESULTS. 

Statement  of  Analysis. — The  composition  of  water 
is  generally  expressed  in  terms  of  a  unit  of  weight  in  a 
definite  volume  of  liquid,  but  no  fixed  standard  is  used, 
the  proportions  being  expressed  by  some  analysts  in 
parts  per  million,  by  others  in  parts  per  hundred  thou- 
sand. Sometimes,  generally  by  English  chemists,  the 
figures  are  given  in  grains  per  imperial  gallon  of  70,000 
grains ;  less  frequently,  in  grains  per  U.  S.  gallon  of 
58,328  grains. 

In  order  to  pass  judgment  upon  the  analytical  re- 
sults from  a  sample  of  water,  the  analyst  must  know 
to  which  class  of  water  it  belongs — whether  river-water, 
well-water,  or  artesian-well  water.  He  must  know 
something  of  the  soil  and  geological  character  of  the 
locality  from  which  the  water  is  obtained,  as  well  as 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       22 5 

other  conditions  of  the  locality  which  might  affect  the 
quality  of  the  water,  such  as  proximity  of  stables,  cess- 
pools, sewers,  factories,  etc. 

Color. — Water  of  the  highest  purity  is  clear,  color 
less,  odorless,  and  nearly  tasteless.  But  the  color  of 
water  is  no  indication  of  its  quality.  A  turbid  or  col- 
ored water  is  not  necessarily  a  dangerous  one,  neither 
is  a  clear,  colorless  water  always  a  safe  water. 

Odor. — For  comfort,  if  for  nothing  else,  potable 
water  should  be  free  from  odor.  Water  sometimes  has 
an  unpleasant  odor  and  taste,  yet  it  may  be  used  with 
perfect  safety  for  domestic  purposes.  At  other  times 
the  odor  may  give  rise  to  suspicions  which  a  subsequent 
examination  may  confirm.  Thus  by  the  odor  alone 
the  safety  of  the  water  cannot  be  told. 

Total  Solids. — This  is  intended  to  represent  the 
total  solid  matters  dissolved  in  the  water;  but  since 
much  of  the  organic  matter  as  well  as  some  of  the  in- 
organic matter  is  volatilized  by  evaporation,  the  total 
solids  obtained  by  this  method  are  only  the  total  non- 
volatile solids.  The  indication  is  thus  lower  than  it 
should  be.  On  the  other  hand,  certain  salts,  especially 
calcium  sulphate,  retain  water  of  crystallization,  thus 
producing  an  effect  in  the  opposite  direction. 

The  total  solids  so  obtained,  contain  both  organic 
and  inorganic  matters,  either  of  which  may  be  injurious 
or  not.  Mineral  waters  contain  large  quantities  of  in- 
organic salts.  Much  smaller  quantities  of  total  solids 
in  other  waters  might  indicate  pollution. 

Large  quantities  of  mineral  solids,  especially  of 
marked  physiological  action,  are  known  to  render  water 
non-potable ;  but  no  absolute  maximum  or  minimum 
can  be  assigned  as  the  limit  of  safety.  An  arbitrary 


226      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

limit  has,  however,  been  fixed  by  sanitary  authorities 
of  60  parts  per  100,000  ;  and  if  the  solid  residue  does 
not  exceed  57  parts  per  100,000,  there  is  no  reason  for 
rejecting  a  water.  Many  waters,  especially  artesian 
waters,  which  are  in  constant  use,  contain  much  larger 
quantities. 

The  loss  on  ignition* should  never  reach  50  per  cent 
of  the  total  residue. 

Chlorine  in  potable  waters  is  very  largely  derived 
from  sodium  and  potassium  chlorides  of  urine  and 
sewage. 

Food  contains  considerable  amounts  of  chlorides, 
and  still  more  is  added  by  way  of  condiment  in  the 
shape  of  salt.  The  chlorine  thus  taken  into  the 
system  is  again  thrown  off  in  the  excreta,  and  thus  ap- 
pears in  the  sewage ;  hence  the  presence  of  large  quan- 
tities of  chlorine  in  water  is  taken  as  an  indication  of 
pollution.  Urine  contains  about  500  parts  of  chlorine 
per  100,000.  The  average  quantity  found  in  sewage  is 
about  11.5  parts  per  100,000.  Over  5  parts  per  100,000 
of  chlorine  in  a  water  may  be  considered,  in  most 
cases,  to  be  due  to  pollution  of  the  water  by  sewage  or 
animal  excretions.  The  chlorine  itself  is  not  a  dan- 
gerous constituent  of  water,  but  its  presence  in  large 
quantities  is  an  unfavorable  indication.  Nevertheless 
too  much  dependence  must  not  be  put  upon  the 
amount  of  chlorine  in  water  as  a  means  of  judging  of 
its  purity,  for  dangerous  vegetable  matter  may  exist  in 
it  without  its  presence  being  indicated  by  chlorine. 
The  maximum  amount  of  chlorine  per  100,000,  given 
by  the  Rivers  Pollution  Commission,  is  21.5  parts,  the 
minimum  6.5  parts.  Various  conditions,  however, 
which  affect  the  proportion  of  chlorine,  such  as  the 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       227 

nature  of  the  strata  through  which  the  water  passes, 
proximity  to  the  sea,  etc.,  must  be  taken  into  account. 

Nitrogen  in  Ammonia. — Ammonium  compounds 
are  usually  the  result  of  the  spontaneous  putrefactive 
fermentation  of  nitrogenous  organic  matter;  nitrites 
are  then  formed,  and  finally  nitrates.  Ammonium  com- 
pounds may  also  result  from  the  reduction  of  nitrites 
and  nitrates  in  the  presence  of  excess  of  organic  matter. 
Therefore  in  either  case  the  presence  of  ammonia  sug- 
gests contamination. 

This  fact  is  so  generally  conceded  that  the  estima- 
tion of  ammonia  in  water,  is  a  very  important  part  of 
the  sanitary  examination. 

In  the  water  from  deep  wells  an  excess  of  ammonia 
is  nearly  always  found,  but  its  presence  here  cannot 
always  be  considered  an  adverse  condition,  since  it  is 
derived  largely  from  the  decomposition  of  nitrates, 
and  shows  previous  contamination ;  but  the  water  hav- 
ing undergone  extensive  filtration  and  oxidation,  its 
organic  matter  is  presumably  converted  into  harmless 
bodies. 

Rain-water  often  contains  large  proportions  of  am- 
monium compounds,  which  it  dissolves  out  of  the  air 
in  its  descent ;  but  here  also,  this  fact  cannot  condemn 
the  water,  since  it  does  not  indicate  contamination 
with  dangerous  organic  matter. 

An  average  of  71  samples  of  rain-water  collected  in 
England  contained  0.05  parts  per  100,000,  including 
an  exceptional  maximum  of  0.21  parts. 

Fischer  ("  Chemische  Technologic  des  Wassers") 
gives  two  analyses  of  typically  good  wells,  containing 
respectively  0.048  and  0.044  parts  per  100,000,  and  of 


228      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

two   typically   bad    shallow   wells,    containing   respec- 
tively 0.084  and  2.227  parts  per  100,000. 

Albuminoid  Ammonia. — If  water  yields  no  albu- 
minoid ammonia  it  is  free  from  recently  added  organic 
contamination.  If  it  contain  more  than  o.oi  part  per 
100,000  it  is  looked  upon  as  suspicious,  and  when  it 
reaches  0.015  parts  per  100,000  it  is  to  be  condemned. 
When  free  ammonia  is  present  in  considerable  quan- 
tity, then  the  albuminoid  ammonia  becomes  suspicious 
when  it  reaches  0.005  parts  per  100,000.  An  opinion 
should  not,  however,  be  formulated  without  a  knowl- 
edge of  the  source  of  the  water;  for,  as  has  been  said 
before,  free  ammonia  may  exist  in  large  quantities  in 
deep  wells  without  indicating  contamination.  Wanklyn 
gives  the  following  standards: 

High  purity ooo    to  .0041  of  albuminoid  ammonia  per  100,000 

Satisfactory  purity    .004110.0082"  "  "  "         " 

Impure  over  .0082  "  "  " 

In  the  absence  of  free  ammonia  he  does  not  condemn 
a  water  unless  the  albuminoid  ammonia  exceeds  .0082 
parts  per  100,000;  but  he  condemns  a  water  yielding 
0.0123  parts  of  albuminoid  ammonia,  under  all  circum- 
stances. 

Nitrogen  as  Nitrates. — Nitrates  are  normally  pres- 
ent in  all  natural  waters,  and  are  derived  chiefly  from  the 
oxidation  of  animal  matters.  The  nitrogen  of  organic 
matters  liberated  by  putrefaction,  is  first  converted 
into  ammonia;  then  this  is  oxidized  into  nitrous,  and 
finally  into  nitric  acid.  These  changes  are  due  partially 
to  direct  oxidation  and  partially  to  certain  micro- 
organisms which  have  the  power  of  converting  nitro- 
genous organic  matter  into  nitrites  and  nitrates. 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.       22Q 

Nitrates  and  nitrites  in  themselves,  in  the  quantity  in 
which  they  exist  in  water,  are  perfectly  harmless.  They 
are,  however,  an  indication  of  previous  contamination  ; 
and  many  analysts  believe  that  a  water  which  has 
once  been  contaminated  is  always  open  to  suspicion. 
Others  consider  them  of  little  importance  in  determin- 
ing the  impurity  of  a  water.  Water  which  is  laden 
with  organic  matter  is  purified  by  percolating  through 
the  ground,  the  nitrogenous  matter  being  converted 
into  nitrates ;  therefore  deep  wells  may  contain  large 
quantities  of  nitrates  without  being  essentially  impure, 
while  the  water  from  shallow  wells  should  be  con- 
demned if  the  nitrates  are  excessive. 

Certain  strata,  as  the  chalk  formation,  yield  large 
amounts  of  nitrates  to  water.  If  the  nitrogen  as 
nitrates  exceeds  0.6  parts  per  100,000  the  water  is 
suspected. 

Nitrogen  as  Nitrites. — Some  chemists  regard  the 
presence  of  nitrites  as  an  indication  that  the  oxidation 
of  the  dangerous  compounds  has  probably  been  in- 
complete, and  accordingly  condemn  water  in  which 
nitrites  are  found.  Leeds  places  the  nitrites  in  Ameri- 
can rivers  at  .03  per  100,000.  The  average  in  good 
waters  is  placed  at  about  .0014  per  100,000.  When 
the  quantity  exceeds  .02  parts  per  100,000  it  is  con- 
sidered an  indication  of  previous  contamination. 

Oxygen  Consuming  Power. — This  is  intended  to 
represent  the  oxidizable  organic  matter  in  the  water. 
But  there  are  other  substances  in  water  besides  organic 
matters  which  absorb  oxygen,  namely,  nitrites,  which 
are  thus  oxidized  to  nitrates ;  ferrous  salts,  which  are 
oxidized  into  ferric  salts  ;  etc.  Thus  the  oxygen-con- 
suming power  does  not  represent  the  organic  matter 


230      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

alone,     However,  .a  water  having  a  high  oxygen-con- 
suming power  may  be  considered  as  polluted. 

The  following  basis  for  interpreting  results  of  this 
method  are  given  by  Frankland  and  Tidy : 

Oxgen  absorbed  in  3  hours. 

High  organic  purity .05  parts  per  100,000 

Medium  purity 05  to  .15      "       "         " 

Doubtful 15  to  .21      " 

Impure over  .21      "       "         " 

Phosphates. — Sewage  contains  large  amounts  of 
phosphates,  but  water  usually  contains  alkaline  or 
earthy  carbonates,  which  precipitate  the  phosphates ; 
therefore  the  absence  of  phosphates  does  not  indicate 
purity.  But  their  presence  may  indicate  sewage  con- 
tamination. .06  parts  per  100,000  is  regarded  with  sus- 
picion (calculated  as  PO4). 

Hardness. — On  account  of  the  presence  of  con- 
siderable amounts  of  calcium  compounds  in  our  food 
sewage  is  usually  very  hard,  containing  especially 
calcium  sulphate.  The  hardness  of  water,  -therefore, 
has  some  bearing  upon  the  question  as  to  whether  the 
water  is  probably  polluted  with  sewage  or  not.  But 
water  may  be  hard,  yet  otherwise  perfectly  pure.  The 
test  for  the  degree  of  hardness  is  therefore  of  little 
importance  in  determining  sewage,  as  the  figures  below 
show  that  water  uncontaminated  by  sewage  may  be 
very  hard. 

Temporary.    Permanent. 

Rain-water,  average o.  3  1.7 

Highest  from  different  geological  formations  . . .  38.6  48.5 
From   272  samples  of  water  from  shallow  and 
polluted  wells  : 

Minimum o  3.8 

Maximum 52  164.3 

Average 19  31.5 


^ 

A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       231 

^ 


The  above  figures  are  parts  in  100,000.  The  hard- 
ness has,  however,  much  significance  from  an  economic 
point  of  view.  Hard  water  is  objectionable  for  domes- 
tic purposes  in  washing,  because  of  its  soap-destroying 
power,  and  for  manufacturing  purposes  in  boilers.  It 
has  no  bad  effect  upon  the  health,  but  is  by  some  con- 
sidered wholesome. 

Standards.  —  Certain  standards  have  been  fixed  by 
some  chemists  for  determining  the  purity  or  impurity 
of  water,  according  to  which  if  certain  figures  are  ex- 
ceeded the  water  is  to  be  condemned. 

Dr.  Tidy's  classification  depends  upon  the  amount 
of  oxygen  consumed,  from  potassium  permanganate, 
after  standing  three  hours. 

1.  Great  organic  purity.  .  .   ......  o       to  0.05 

2.  Medium  purity  ...............   0.05    "0.15 

3.  Doubtful  ...................   0.15    "0.21 

4.  Impure  ....................        over  0.2  1 

These  standards  are  applied  to  waters  other  than 
upland  surface-waters,  in  which  larger  quantities  of 
oxygen  may  be  absorbed. 

Wanklyris  standard  is  based  upon  the  indications  of 
the  amounts  of  free  and  albuminoid  ammonia,  as 
follows  : 

1.  Extraordinary  purity  ........  o         to  0.005  part  albuminoid  NH3. 

2.  Satisfactory  purity.  ,  ........  0.005  to  o.oio    "  "  " 

3.  Dirty  ...........    ..........         over  o.oio    "  "  " 

If  the  albuminoid  ammonia  exceeds  0.005  parts  per 
100,000  the  free  ammonia  must  be  taken  into  account. 
If  the  free  ammonia  is  in  large  quantity  it  is  a  sus- 
picious sign.  If  it  is  in  small  quantity  or  altogether 
absent,  the  water  should  not  be  condemned,  unless  the 


232      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 


albuminoid  ammonia  is  something  like  o.oio  parts  per 
100,000;  while  over  0.015  should  condemn  the  water 
absolutely. 

The  following  is  a  list  of  analyses  of  waters  which 
were  pronounced  good.  The  results  are  given  in  parts 
per  100,000. 


"l. 

II. 

ill. 

IV. 

Chlorine                               . 

o  877 

i  ^33 

92Q/1 

i  «;78 

Free  ammonia.  

o  0004 

none 

O  OO2 

O  OOO2 

Albuminoid  ammonia  

none 

0.0006 

O  OO5 

O  OO22 

Oxygen  absorbed  (in  3  hours) 
N  in  nitrates  and  nitrites.... 

0.0054 
0.2525 

IQ.23 

0.0016 
0.3376 
14.0000 

0.0255 
O.OIO7 
I  q  aq 

O.OOOS 
0.2633 
2  O7Q 

Permanent  hardness 

o  7ic 

3Q^d 

3  060 

1   080 

Organic  and  volatile  matters 
Total  solids  (dried  at  230°  F.) 

1.5 

24.4 

i,7 

27 

trace 
37.40 

2.IOO 
9.40 

The  following  were  pronounced  bad  : 


I. 

II. 

III. 

IV. 

0.316 

62.43 

4.208 

28.230 

0.0196 

0.278 

none 

0.0105 

0.0678 

O.OO3O 

0.0105 

0.030"$ 

Oxygen  absorbed  (in  3  hours) 
N  in  nitrates  and  nitrites  
Total  hardness  

0.2912 
0.0283 
6.940 

0.133 
none 
27.72 

0.0165 
0.247 
13.068 

O.2IIO 
O.62TO 
5O.OO 

Permanent  hardness  

q  e 

23.76 

2.574 

32.670 

Organic  and  volatile  matters 
Total  solids  (dried  at  230°  F.) 

0-5 
15.60 

19-5 
156.20 

trace 

30.50 

8.00 
146.50 

I,  Back  of  slaughter-house  ;  II,  Drive-well  on  beach  ;    III,  Well  ; 
IV,  Well  30  feet  deep. 


A.  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.      233 


CHAPTER   XV. 

ESTIMATION   OF   CARBONIC-ACID   GAS   IN   THE 
ATMOSPHERE. 

THIS  is  done  by  Pettenkofer's  method.  A  glass 
globe  or  bottle  holding  from  5  to  10  litres  is  filled  with 
the  air  to  be  tested,  by  means  of  a  bellows  ;  baryta 
water  of  known  strength  is  then  introduced  in  con- 
venient quantity. 

The  bottle  is  then  securely  closed  and  set  aside  for 
about  one  hour,  rotating  it  at  intervals,  so  that  the 
liquid  is  spread  over  the  entire  inner  wall  of  the  bottle. 

When  the  time  is  up  the  baryta  water  is  emptied  out 
quickly  into  a  beaker,  covered  carefully  with  a  watch- 
glass,  and  when  the  barium  carbonate  has  subsided  a 
portion  of  the  clear  liquid  is  withdrawn  and  titrated 

N 

with  —   oxalic-acid  solution.     The  difference  between 
10 

the  quantity  of  oxalic-acid  solution  required  to  neu- 
tralize the  barium-hydroxide  solution,  before  and  after 
contact  with  the  air,  is  the  quantity  equivalent  to  the 
carbonic-acid  gas  absorbed. 

The  Baryta-water  is  made  by  dissolving  about  7 
gms.  of  pure  crystallized  barium  hydroxide  in  1000  cc. 
of  distilled  water. 

This  solution,  being  prone  to  absorb  CO3  out  of  the 
air,  must  be  kept  in  a  special  bottle,  such  as  is  illus- 
trated in  Fig.  23,  which  prevents  access  of  COa  and 


234      A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

admits  of  the  withdrawal  of  any  quantity  of  solution 
without  inverting  the  bottle. 

The  Bottle  which  is  used  to  collect  the  air  should 
hold  from  5  to  10  litres,  and  its  exact  capacity  must  be 
known.  This  may  be  found  by  filling  the  bottle  to 
the  bottom  of  the  cork  with  water  and  then  accurately 
measuring  the  water.  Before  using  the  bottle  it  must 
be  absolutely  dry. 

The  Analysis. — Into  the  bottle/  the  capacity  of  which 
is  exactly  known, — we  will  assume  it  to  be  7100  cc., — 
is  blown  the  air  to  be  tested,  by  means  of  a  bellows. 

100  cc.  of  the  baryta-water  are  then  introduced,  thus 
leaving  7000  cc.  of  air  in  the  bottle. 

The  bottle  is  now  securely  closed  and  set  aside  for 
about  half  an  hour,  rotating  it  occasionally  so  as  to 
spread  the  liquid  over  the  entire  inner  wall  of  the 
bottle.  While  waiting  for  the  half-hour  to  expire,  a 
convenient  quantity  of  baryta-water  is  taken  and  its 
strength  compared  to  decinormal  oxalic-acid  solution 
by  titrating  with  the  latter,  using  phenolphthalein  as 
indicator. 

50  cc.  of  baryta-water  is  a  convenient  quantity. 
This  is  placed  in  a  beaker,  a  few  drops  of  phenolphtha- 

N 

lein  added,  and  then  titrated  with  the  —  acid  solution 

10 

until  the  color  just  disappears. 

Let  us  assume  that  40  cc.  of  the  latter  were  con- 
sumed ;  80  cc.  will  then  be  consumed  by  100  cc.  of 
baryta-water. 

Ba(OH)2  +  H2C204  +  2H2O  =  BaC2O4  +  4H2O  ; 
2)170.9  2)126 

10)  85.45  ioj~63  N 

8-545  gms.          6.3  gms.  or  1000  cc.  —  V.  S. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       235 

Ba(OH),  +  CO,  =  BaCO,+  HaO. 
2)170.9  2)44 

IP)    85.45  10)22 

8.545  gnis.        2.2  gms. 


These  equations  show  that  2,2  gms.  of  carbon  di- 
oxide will  neutralize  as  much  barium  hydroxide  as 

N 

1000  cc.  of  —  oxalic-acid  solution.     And  thus  each  cc. 
10 

of  the  --  oxalic-acid  solution  is  chemically  equivalent 

to  0.0022  gm.  of  carbon  dioxide ;  therefore  100  cc.  of 
the  baryta-water  is  capable  of  absorbing  80  X  .0022 
gm.  =  0.176  gm,  of  CO2. 

The  next  step  is  to  determine  the  quantity  of  CO, 
that  was  absorbed  by  the  100  cc.  of  baryta-water,  which 
was  introduced  into  the  bottle  of  air. 

The  liquid  is  poured  out  of  the  bottle  into  a  small 
beaker,  carefully  covered  with  a  watch-glass,  and  the 
barium  carbonate  allowed  to  settle.  Then  50  cc.  of 
the  clear  supernatant  liquid  are  drawn  out  of  the  beaker 
by  means  of  a  pipette,  treated  with  a  few  drops  of 

N 
phenolphthalein  T.  S.,  and  titrated  with  the  —  oxalic 

acid  V.  S.  until  the  red  color  is  just  discharged.  Note 
the  number  of  cc.  consumed,  double  it,  and  deduct  this 
number  from  80,  the  quantity  which  100  cc.  of  baryta- 
water  consumed  before  being  brought  in  contact  with 
CO,; 

Example. — Assuming  that  30  cc.  of  the  oxalic-acid 
solution  were  required  by  the  50  cc.  of  the  baryta- 
water  after  exposure,  the  100  cc.  then  would  require 
60.  There  is  thus  a  loss  of  alkalinity  equivalent  to  20 


236      A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

N 

cc.  of  —  oxalic  acid  V.  S.     This  is  due  to  the  absorp- 
10 

tion  of  carbon  dioxide,  which  neutralizes  the  hydroxide 
by  forming  a  carbonate. 

N 

Now  since  each  cc.  of  —  oxalic  acid  V.  S.  is  chemi- 
10 

cally  equivalent   to  0.0022    gm.    of   CO2,  the  baryta- 
water  must  have  absorbed 

20  X  0.0022  gm.  —  0.044  gm-  °f  CO2. 

Therefore  the  7000  cc.  of  air  which  the  bottle  held 
contained  0.044  gm-  of  CO3. 

In  stating  the  result  of  an  analysis  the  quantity  of 
CO3  by  volume  in  10,000  cc.  of  air  is  generally  given. 

In  the  above  case  7000  cc.  of  air  contained  0.044  gm. 
of  COa;  10,000  cc.  of  this  same  air,  then,  contains 

0.044  X  10,000  0.044  X  10 

or  =  0.0628  gm. 

7000  7 

If  several  bottles  are  in  use  it  is  convenient  to  mark 
upon  them  the  multiplier  and  divisor;  thus: 

10,000  10 

7000  ~7~* 

In  calculating  the  volume  of  a  gas,  the  temperature 
and  pressure  must  be  taken  into  account. 

By  referring  to  the  following  table  the  volume  occu- 
pied by  o.ooi  gm.  of  CO,  at  different  temperatures  can 
be  seen. 

The  volume  of  0.0628  gm.  of  CO2  at  16°  C.  is 

0.0628  X  Q.53843  =       gl  cc 

O.OOI  JJ 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.      237 


TABLE  SHOWING  VOLUME  OF  .001  GM.  OF  CARBON  DIOXIDE  AT 
VARIOUS  TEMPERATURES. 


C.° 

F.° 

Cc. 

C.° 

F.° 

Cc. 

0 

32 

0.50863 

13 

55-4 

0.53314 

I 

33.3 

0.51049 

14 

57-2 

0.53471 

2 

35-6 

0.51235 

15 

59 

0.53657 

3 

37-4 

0.5I45I 

16 

60.8 

0.53843 

4 

39-2 

0.51608 

17 

62.6 

0.54030 

5 

41 

0.51794 

18 

64,4 

0.54216 

6 

42.8 

0.51980 

19 

66.2 

0.54402 

7 

44.6 

0.52167 

20 

68 

0.54589 

8 

46.4 

0.52353 

21 

69.8 

0-54775 

9 

48.2 

0.52539 

22 

71.6 

0.54961 

10 

50 

o.  52726 

23 

73-4 

0.55177 

ii 

51-8 

0^52912 

24 

75-2 

0-55334 

12 

53-6 

0.53098 

If  the  pressure  remains  constant,  the  volume  of  a 
gas  increases  regularly  as  the  temperature  increases, 
and  decreases  as  the  temperature  decreases.  (Charles' 
Law.) 

This  expansion  or  contraction  amounts  to-g-^  of  the 
volume  of  the  gas  for  each  degree  centigrade. 

Thus  by  calculation  the  volume  of  .001  gm.  COa 
(0.50863  cc.)  at  any  temperature  may  be  found. 


of  .50863  =  0.001863. 


Then  to  find  the  volume  at  any  given  C.  temperature 
multiply  the  degree  of  temperature  by  0.001863,  and 
add  the  answer  to  0.50863. 


238       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


CHAPTER  XVI. 

ESTIMATION   OF   ALCOHOL   IN   TINCTURES   AND 
BEVERAGES. 

THE  quantity  of  alcohol  contained  in  dilute  spirit, 
which  leaves  no  residue  upon  evaporation,  may  be 
ascertained  by  taking  the  sp.  gr.  and  referring  to  the 
alcohol  table.  When  taking  the  specific  gravity,  the 
temperature  of  the  liquid  should  be  15^°  C.  (60°  F.). 

In  Wines,  Beer,  Tinctures,  and  other  alcoholic 
liquids  containing  vegetable  matter,  the  sp.  gr.  of  the 
sample  is  taken  at  15^°  C.  (60°  F.)  and  noted.  A  cer- 
tain quantity  (say  100  cc.)  is  measured  off  and  evapo- 
rated to  one  half,  or  till  all  odor  of  alcohol  has  passed 
off,  the  evaporation  being  conducted  without  ebullition, 
in  order  that  particles  of  the  material  may  not  be  car- 
ried off  by  the  steam.  The  liquid  left  is  then  diluted 
with  distilled  water,  cooled  to  60°  F.  and  made  up  to 
the  original  volume  (100  cc.),  and  the  sp.  gr.  taken. 
Lastly,  we  calculate :  the  sp.  gr.  before  evaporating  is 
divided  by  the  sp.  gr.  after  evaporating,  and  the  quo- 
tient will  be  the  sp.  gr.  of  the  water  and  alcohol  only 
of  the  liquor.  Then  by  referring  to  the  alcohol  table 
the  percentage  of  alcohol  contained  in  the  liquor  is 
obtained. 

Example. — The  liquor  before  evaporating  had  a  sp. 
gr.  of  0.9951  ;  after  evaporation  and  dilution  to  100  cc. 
the  sp.  gr.  was  found  to  be  1.0081. 


A  TEXT-BOOK   OF   VOLUMETRIC'  ANALYSIS.       239 

-—  =  0.987,  the  sp.  gr.  of  the  contained  spirit. 

Then  by  referring  to  the  table  we  will  find  that  this 
sp.  gr.  corresponds  to  7.33  per  cent.,  by  weight,  of  abso- 
lute alcohol. 

Another  Way  is  to  boil  the  liquid  in  a  retort,  con- 
dense the  vapor,  and  when  all  the  alcohol  has  passed 
over  add  sufficient  water  to  the  distillate  to  make  up 
the  original  volume,  at  the  temperature  of  I5|-0  C. 
(60°  F.).  Then,  by  taking  the  sp.  gr.  of  this  diluted 
distillate,  the  quantity  of  absolute  alcohol  is  found  by 
reference  to  the  table.  This  latter  method  requires 
the  taking  of  the  sp.  gr.  but  once  and  gives  more  ac- 
curate results. 


240       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


TABLE  FOR  ASCERTAINING  THE  PERCENTAGES  RESPECTIVELY  OF 
ALCOHOL  BY  WEIGHT,  BY  VOLUME,  AND  AS  PROOF  SPIRIT, 
FROM  THE  SPECIFIC  GRAVITY. 

Condensed  from  the  excellent  Alcohol  Tables  of  Mr.  Hehner  in  the 
" 'Analyst :,"  vol.  v.  pp.  43-63. 


Specific 
Gravity 
15-5°. 

Absolute 
Alcohol 
by  w'ght. 
Per  cent. 

Absolute 
Alcohol 
jy  vol'me 
Percent. 

Proof 
Spirit. 
Per  cent. 

Specific 
Gravity 
15.5'. 

Absolute 
Alcohol 
by  w'ght. 
Per  cent. 

Absolute 
Alcohol 
by  vol'me 
Per  cent. 

Proof, 
Spirit. 
Percent. 

J.OOOO 

o.oo 

o.oo 

o.oo 

.9489 

35-05 

41.90 

73-43 

•9999 

0.05 

0.07 

0.12 

•9479 

35-55 

42-45 

74-39 

.9989 

0.58 

o-73 

1.28 

•9469 

36.06 

43.01 

75-37 

-9979 

1.  12 

1.42 

2.48 

•9459 

36.61 

43-63 

76.45 

.9969 

i-75 

2.20 

3-85 

•9449 

37-17 

44.24 

77  53 

•9959 

2-33 

2.93 

5-13 

•9439 

37-72 

44.86 

78.61 

•9949 

2.89 

3.62 

6.34 

.9429 

38.28 

45-47 

79.6,8 

•9939 

3-47 

4-34 

7.61 

.9419 

38-83 

46.08 

80.75 

.9929 

4.06 

5-o8 

8.90 

•9409 

39  35 

46.64 

81.74 

.9919 

4.69 

5-86 

10.26 

•9399 

39-85 

47.18 

82.69 

.9909 

5-3i 

6.63 

11.62 

.9389 

40-35 

47.72 

83.64 

.9899 

5-94 

7.40 

12.97 

•9379 

40-85 

48.26 

84.58 

.9889 

6.64 

8.27 

14.50 

•9369 

41-35 

48.80 

85-5.1 

.9879 

7-33 

9-i3 

15-99 

•9359 

41-85 

49-34 

86.47 

.9869 

8.00 

9-95 

'7-43 

•9349 

42-33 

49.86 

87.37 

.9859 

8.71 

10.82 

18.96 

•9339 

42.81 

50-37 

88.26 

.9849 

9-43 

11.70 

20.50 

•9329 

43.29 

50.87 

89.15 

•9839 

10.15 

12.58 

22.06 

•9319 

43.76 

51-38 

90.03 

.9829 

10.92 

I3-52 

23.70 

•93°9 

44  23 

51-87 

90.89 

.9819 

11.69 

14.46 

25-34 

•9299 

44.68 

52-34 

91-73 

.9809 

12.46 

15.40 

26.99 

.9289 

45-M 

52.82 

92.56 

•9799 

13-23 

16.33 

28.62 

.9279 

45-59 

53-29 

9339 

.9789 

14.00 

17.26 

30.26 

.9269 

46.05 

53-77 

94.22 

•9779 

14.91 

18.36 

32.19 

•9259 

46.50 

54-24 

95-os 

.9769 

15-75 

19-39 

33-96 

•9249 

46.96 

54-7i 

95-88 

•9759 

16.54 

20.33 

35-63 

•9239 

474i 

55-i8 

96.70 

•9749 

17-33 

21.29 

37-30 

.9229 

47-86 

55-65 

97-  52 

•9739 

18.15 

22.27 

39-03 

.9219 

48.32 

56.11 

98.34 

.9729 

18.92 

23.19 

40.64 

.9209 

48.77 

56.58 

99.16 

.9719 

Q7OQ 

19-75 
20.58 

24.18 

2C.I7 

42.38 
44.12 

.9199 

49.20 

57.02 

99-93 

•y/^y 

21.38 
22.15 

•^.V1/ 
26.13 
27.04 

45-79 
4£'3£ 

.9198 

49-24 

57.06 

loo.ooPs 

.9679 

22.92 

27-95 

48.98 

.9669 

23-69 

28.86 

50-57 

.9189 

49-68 

57-49 

100.76 

•9659 

24.46 

29.76 

52-16 

.9179 

50.13 

57-97 

101.59 

.9649 

25-21 

3065 

53-71 

.9169 

50.57 

58.41 

102.35 

•9639 

25-93 

31.48 

S5-i8 

•9*59 

51.00 

5885 

103.12 

.9629 

26.60 

32.27 

56.55 

.9149 

5!-42 

59.26 

103.85 

.9619 

27.29 

33-06 

57-94 

•9I39 

51-83 

59-68 

104.58 

.9609 

28.00 

33-89 

59-4° 

.9129 

52.27 

60.12 

ios-35 

•9599 

28.62 

3461 

6066 

.9119 

52.73 

60.56 

106.15 

•9589 
•9579 

29.27 
29  93 

35-35 
36.12 

6i.95 
63.30 

9109 
.9099 

53-17 
53-6i 

61.02 
61.45 

106.93 
107.69 

.9569 

30-50 

36.76 

64-43 

.9089 

54-05 

61.88 

108.45 

•9559 

31.06 

37-41 

65-55 

.9079 

54-52 

62.36 

109.28 

•9549 

31.69 

38.11 

66.80 

.9069 

55-0° 

62.84 

[10.12 

•9539 

32.31 

38.82 

68.04 

•9059 

55-45 

63.28 

110.92 

•9529 

32.94 

39-54 

69.29 

.9049 

55-91 

63-73 

111.71 

•95J9 

33-53 

40.20 

70.46 

•9°39 

56.36 

64.18 

112.49 

•95°9 

34.10 

40.84 

71.58 

.9029 

56.82 

64-63 

113.26 

•9499 

34-57 

41.37 

72.50 

.9019 

57-25 

65-05 

"3-99 

A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       241 


Specific 
Gravity 

i5-5c- 

Absolute 
Alcohol 
by  w'ght. 
Per  cent. 

Absolute 
Alcohol 
by  vol'me 
Per  cent. 

Proof 
Spirit. 
Per  cent. 

Specific 
Gravity 
15-5°. 

Absolute 
Alcohol 
by  w'ght. 
Per  cent. 

Absolute 
Alcohol 
by  vol'me 
Percent. 

Proof 
Spirit. 
Percent. 

.9009 

57-67 

65-45 

11469 

.8429 

82.19 

87.27 

!52.95 

.8999 

58.09 

6585 

115.41 

.8419 

82.58 

87.58 

153-48 

.8989 

58.55 

6629 

116.18 

.8409 

82.96 

87.88 

154-01 

.8979 

59.00 

66.74 

116.96 

•8399 

83-35 

88.19 

x54-54 

.8969 

59-43 

6715 

117.68 

.8389 

83-73 

88.49 

'SS-o? 

•8959 

59.87 

67-57 

118.41 

-8379 

84.12 

8879 

15561 

.8949 

60.29 

67.97 

119.12 

.8369 

8452 

89.11 

156.16 

•8939 

60  71 

68.36 

119.80 

•8359 

84.92 

89.42 

156.71 

.8929 

61.13 

68.76 

120.49 

•8349 

85-31 

89.72 

*57-24 

.8919 

61.54 

69.15 

121.  18 

.8339 

85-69 

90.02 

I57-76 

.8909 

61.96 

69-54 

121.86 

.8329 

86.08 

90.32 

158  28 

.8899 

62.41 

69.96 

122.  6r 

.8319 

86.46 

90.61 

15879 

.8889 

62.86 

70.40 

123.36 

.8309 

8685 

90.90 

J59-3r 

.8879 

63-3° 

70.81 

124.  OQ 

.8299 

87.23 

91.20 

159.82 

.8869 

63-74 

71.22 

124.80 

.8289 

87.62 

91.49 

160.33 

.8859 

64.17 

71.62 

!25.5I 

.8279 

88.00 

91.78 

160.84 

.8849 

64.61 

72.02 

126.22 

.8269 

88.40 

92.08 

161.37 

.8839 

65.04 

72.42 

126.92 

.8259 

88.80 

92-39 

161.91 

.8829 

65.46 

72.80 

127-59 

.8249 

89.19 

92.68 

162.43 

.8819 

65.88 

73-*9 

128.25 

.8239 

89.58 

92.97 

162.93 

.8809 

66.30 

73-57 

128.94 

.8229 

89.96 

93-26 

l63-43 

.8799 

66.74 

73-97 

129.64 

.8219 

90-32 

93-52 

163.88 

.8789 

67.17 

74-37 

I30-33 

.8209 

90.68 

93-77 

164.33 

•8779 

67.58 

74-74 

130.98 

.8199 

91.04 

94-°3 

164.78 

.8769 

68.00 

75-12 

131.64 

.8189 

91-39 

94.28 

165.23 

.8759 

68.42 

75-49 

132.30 

.8179 

9J-75 

94-53 

165.67 

•8749 
•8739 

68.83 
69.25 

75-87 
76.24 

I32-95 
I33-60 

.8169 
.8159 

92.11 
92.48 

94-79 
95.06 

166.12 
166.58 

.8729 

69.67 

76.61 

I34-25 

.8149 

92.85 

95-32 

167.04 

.8719 

70.08 

76.98 

I34-90 

.8139 

93-22 

95-58 

167.50 

.8709 

70.48 

77-32 

I35-5I 

.8129 

93-59 

95-84 

167.96 

.8699 

70.88 

77.67 

136.13 

.8119 

9396 

96.11 

168.24 

.8689 

71.29 

78.04 

136.76 

.8109 

94-31 

96.34 

168.84 

.8679 

71.71 

78.40 

J37-40 

.8099 

94.66 

96-57 

169.24 

.8669 

72.13 

78.77 

138-05 

.8089 

95-00 

96.80 

169.65 

.8659 

72-57 

79-16 

138.72 

.8079 

95-36 

97-05 

170.07 

.8649 

73.00 

79-54 

13939 

.8069 

95-71 

97.29 

170.50 

.8639 

73-42 

79.90 

140.02 

.8059 

96.07 

97-53 

170.99 

.8629 

73-83 

8026 

140.65 

.8049 

96.40 

97-75 

171.30 

.86x9 

74-27 

80.64 

Mi-33 

.8039 

96.73 

97.96 

171.68 

.8609 

74-73 

81.04 

142.03 

.8029 

97.07 

98.18 

172.05 

.8599 

75-iS 

81.44 

M2.73 

.8019 

97.40 

98.39 

172.43 

.8589 
•8579 

75-64 
7608 

81.84 
82.23 

M3  42 
144.10 

.8009 
•7999 

97-73 
98.06 

98.61 
98.82 

172.80 
i73-'7 

.8569 

76.50 

82.58 

144  72 

.7989 

98.37 

9900 

I73-50 

•8559 

76.92 

82.93 

MS-  34 

-7979 

98.69 

99.18 

173-84 

.8549 

77-33 

83.28 

145-96 

.7969 

99.00 

99-37 

174.17 

•8539 

77-75 

83.64 

H6-57 

•7959 

99-32 

99-57 

I74.52 

.8529 

78.16 

83-98 

147.17 

•7949 

99-65 

99-77 

174-87 

•8519 
.8509 

78.56 
78.06 

8431 
84.64 

M7  75 
148.32 

•7939 

99-97 

99.98 

175.22 

•  84Q9 

'       V 

79-36 

(M*V*4 

84.97 

148.90 

8489 

79.76 

85.29 

149.44 

.8479 

80.17 

85.03 

150.06 

Absolute  Alcohol. 

8469 

8058 

8597 

150.67 

•8459 

81.00 

86.32 

151.27 

.8449 

81.40 

86.64 

151.83 

•8439 

81.80 

86.96 

152.40 

•7938 

100.00 

100.00 

1  75-25 

242       A   TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 


CHAPTER  XVII. 

ESTIMATION  OF  TANNIN. 

G.  FLEURY  (Jour.  Phar.  Chim.,  1892,  499)  proposes 
to  use  egg-albumen  for  estimating  tannin  in  wine  and 
in  the  petals  of  red  roses. 

The  hard-boiled  egg-albumen  is  dried  at  a  moderate 
temperature,  and  powdered.  This  is  washed  with 
dilute  alcohol  (10  per  cent),  very  slightly  acidulated 
with  tartaric  acid,  to  saturate  the  alkali.  The  albumen 
is  again  dried,  and  kept  in  a  well-stoppered  bottle. 

The  method  of  operation  is  as  follows : 

Albumen  powder,  equal  to  seven  or  eight  times  the 
quantity  of  tannin,  which  is  supposed  to  be  present,  is 
added  to  the  liquid  in  a  flat  dish.  The  dish  is  then  set 
aside  for  forty-eight  hours,  stirring  occasionally ;  the 
liquid  must  during  this  time  be  acid,  not  alkaline. 

The  end  of  the  reaction  is  attained  when  the  liquid 
ceases  to  give  a  color  with  ferric  chloride  T.  S. 

The  powder  is  then  collected  on  a  filter,  washed  with 
very  dilute  alcohol,  and  then  dried  at  100°  C.  At  the 
same  time  a  sample  of  the  original  powder  is  dried  and 
weighed,  to  determine  the  amount  of  water  it  contains. 

The  increase  in  weight  of  the  albumen  which  was  in 
contact  with  the  tannin,  minus  the  loss  of  weight  of  the 
albumen  in  the  check  experiment,  gives  the  weight  of 
tannin  present. 

This   method  is  not  available    for   determining  the 


A   TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.       243 

tannid  in  nutgalls,  because  the  absorption  by  the  albu- 
men is  incomplete  and  too  slow.  In  testing,  it  must  be 
borne  in  mind  that  gallic  acid  is  not  absorbed  by  the 
albumen,  and  consequently  still  gives  its  reaction  with 
ferric  chloride. 


ESTIMATION  OF  TANNIN  IN  BARKS,  ETC. 
(LOWENTHAL'S  METHOD.) 

The  principle  of  this  method  depends  upon  the  oxi 
dation  of  the  tannic   acid,  together  with  other  easily 
oxidizable  substances,  by  titrating  with  potassium  per- 
manganate. 

The  total  amount  of  such  substances  is  thus  found, 
and  expressed  by  a  known  volume  of  permanganate. 
The  actual  available  tannin  is  then  removed  by  gela- 
tine or  glue,  and  another  titration  made,  to  determine 
the  amount  of  oxidizable  matters  other  than  tannin. 

The  difference  between  the  amounts  of  permanga- 
nate solution  used  in  the  two  titrations  gives  the 
amount  of  tannin  present  which  is  available  for  tan- 
ning purposes,  expressed  in  terms  of  permanganate. 

N 

Solutions  Required. — i.  —  Potassium  Permanga- 
nate V.S.  (1.05  gm.  per  litre). 

2.  Indigo  Solution. — 6  gms.  of  pure  precipitated  in- 
digo and  50  cc.  of  concentrated  sulphuric  acid  are  dis- 
solved in  sufficient  water  to  make  one  litre. 

3.  Glue  and  Salt  Solution. — 25  gms.   of  good  trans- 
parent  glue   are    macerated   in    cold  water,  and  then 
heated  to  dissolve ;   the  solution  is  then  made  up  to 
one  litre,  and  saturated  with  common  salt.     The  solu- 
tion should  be  filtered  clear  when  used. 


244       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

4.  Acidified  Solution  of  Common  Salt. — This  is  a  sat- 
urated solution  of  common  salt,  containing  in  one  litre 
25  cc.  of  sulphuric  acid. 

The  Analysis. — 20  gms.  of  the  bark  or  10  gms.  of 
sumach  are  boiled  with  several  portions  of  water  until 
exhausted,  and  the  solution  when  cold  is  made  up  to 
one  litre. 

10  cc.  of  this  solution  are  diluted  to  1000  cc. ;  25 
cc.  of  the  indigo  solution  are  added,  and  the  perman- 
ganate solution  then  run  in,  drop  by  drop,  from  a 
burette,  stirring  constantly,  until  the  blue  color  changes 
to  yellow,  and  the  number  of  cc.  of  permanganate  so- 
lution consumed  noted. 

25  cc.  of  the  indigo  solution  are  now  taken  and  di- 
luted to  1000  cc.,  titrated  with  permanganate,  and  the 
number  of  cc.  again  noted.  By  deducting  this  number 
from  the  number  of  cc.  used  in  the  first  titration,  the 
quantity  of  permanganate  required  by  the  tannin  and 
the  other  oxidizable  substances  in  the  locc.  of  solution 
taken  is  found. 

The  next  step  is  to  deprive  a  portion  of  the  tannin 
solution  of  its  tannin,  and  again  titrate. 

100  cc.  of  the  tannin  solution  are  treated  with  50 
cc.  of  the  glue  and  salt  solution,  and,  after  stirring,  100 
cc.  of  the  acidulated  salt  solution  are  added,  the  mix- 
ture stirred  again,  and  set  aside  for  several  hours.  The 
glue  absorbs  the  tannin  out  of  solution.  The  solution 
is  then  filtered.  The  filtrate  should  be  perfectly  clear. 

Of  this  filtrate  take  50  cc.  (containing  20  cc.  of  the 
tannin  solution),  mix  with  25  cc.  of  the  indigo  solution, 
and  titrate  with  the  permanganate  solution  as  before, 
noting  the  number  of  cc.  consumed. 

Another  25  cc.  of  the  indi-go  solution  are  now  taken, 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.      245 

diluted  as  in  the  other  trial,  and  again  titrated  with 
permanganate.  By  deducting  the  number  of  cc.  so 
obtained  from  the  number  required  by  the  50  cc.  of 
filtrate,  the  quantity  required  by  the  oxidizable  matter 
other  than  tannic  acid  in  the  20  cc.  of  tannin  solution 
is  obtained.  Therefore  one  half  of  this  quantity,  when 
deducted  from  the  quantity  of  permanganate  solution 
representing  the  total  oxidizable  matter  in  10  cc.  of  the 
tannin  solution,  gives  the  quantity  of  permanganate 
which  was  effected  by  the  tannin  above. 

Duplicate  titrations  should  always  be  made,  and 
should  agree  within  o.i  or  0.2  cc.  of  the  permanganate 
solution. 

Thus  far  we  have  only  the  tannin  value  (expressed  in 
terms  of  permanganate),  of  10  cc.  of  the  original  solution, 
representing  T-L-  of  the  material  under  examination. 

The  permanganate  solution  may  be  compared  with 
a  standard  solution  of  the  purest  gallo-tannic  acid  ob- 
tainable, or  with  any  tannin  of  known  value,  and  thus 
a  coefficient  obtained. 

According  to  the  experiments  of  Neubauer,  63  gms. 
of  pure  crystallized  oxalic  acid  (equivalent  to  31.4  gms. 
potassium  permanganate)  correspond  to  41.57  gms.  of 
purified  gallo-tannic  acid  (nutgall  tannin).  And  Oser 
found  that  63  gms.  of  oxalic  acid  correspond  to  62.355 
gms.  of  querci-tannic  acid  (oak-bark  tannin).  These 
coefficients  are  now  largely  used. 

Based  upon  these  figures  each  cc.  of  permanga- 

nate solution  represents  .0013856  gm.  of  gallo-tannin, 
or  .0020785  gm.  of  querci  tannin.  In  most  analyses, 
however,  especially  when  the  composition  of  the  tannin 
is  not  exactly  known,  it  is  expressed  as  oxalic  acid. 


246      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 


CHAPTER   XVIII. 
ESTIMATION  OF  OLEIC  ACID. 

OLEIC  acid  may  be  estimated  volumetrically  by 
standard  solution  of  potassa  or  soda,  using  phenol- 
phthalein  as  an  indicator. 

The  reaction  is  expressed  by  the  following  equa- 
tion: 

C,8HS40,  +  KOH  =  KC..H..O.  +  H,O. 

Oleic  acid. 

N 
282  gms.         56  gms.  or  1000  cc.  —  KOH. 

Thus  each  cc.  of  the  normal  alkali  solution  consumed 
represents  0.282  gm.  of  oleic  acid. 

Estimation  of  Oleic  Acid. — One  gramme  of  the  im- 
pure fatty  acid  is  saponified  in  a  basin  by  heating  with 
a  slight  excess  of  alcoholic  potash,  till  dissolved,  and 
then  diluted  with  water.  This  solution  is  treated  with 
acetic  acid  drop  by  drop,  until  on  stirring  a  faint  per- 
manent turbidity  ensues.  Dilute  solution  of  potassium 
hydrate  is  then  stirred  in  drop  by  drop  till  the  liquid 
just  clears  up,  and  then  solution  of  plumbic  acetate  is 
stirred  in  until  precipitation  ceases.  The  precipitate 
having  been  allowed  to  settle,  the  supernatant  liquor  is 
poured  off  and  the  soap  washed  once  with  boiling  water. 
A  little  clean  sand  is  rubbed  up  with  the  soap  in  the 
basin,  and  the  whole  scraped  out  and  transferred  to  a 
"  Soxhlet,"  in  which  it  is  thoroughly  exhausted  with  90 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       247 

cc.  of  pure  ether.  The  ethereal  solution  (which  now 
contains  only  plumbic  oleate,  the  plumbic  palmitate  and 
stearate  being  left  insoluble  in  the  Soxhlet)  is  trans- 
ferred to  a  special  apparatus,  sold  by  apparatus  vendors 
as  "  Muter's  oleine  tube."  This  is  a  graduated  and 
stoppered  tube  holding  1 20  cc.,  and  having  a  spout  and 
stop-cock  at  30  cc.  from  its  base.  Previously  to  intro- 
ducing the  ether,  place  20  cc.  of  dilute  hydrochloric 
acid  (i  in  3)  into  the  tube,  and  then  make  up  the  whole 
with  ether-rinsings  of  the  basin  to  the  120-cc.  mark. 
Close  the  tube,  shake  well,  and  set  aside.  When  settled, 
note  the  full  volume  of  the  ethereal  solution  of  oleic 
acid,  and  run  off  an  aliquot  part  from  the  tap  into  a 
weighed  dish,  evaporate,  dry  in  the  water-oven,  and 
weigh.  Finally  calculate  this  weight  to  that  of  the 
whole  bulk  of  ethereal  solution  previously  noted,  thus 
getting  the  amount  of  real  oleic  acid  present  in  the 
gramme  of  crude  acid  started  with.  [From  Muter's 
"  Analytical  Chemistry."] 


248      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 


CHAPTER   XIX. 
ANALYSIS  OF  SOAP. 

Estimation  of  Water  and  Volatile  Matters. — 
(a)  10  grns.  of  the  soap  are  dried  to  a  constant  weight  at 
100°  C.  and  carefully  weighed  ;  the  loss  of  weight  = 
water. 

(b)  Free  Fats. — The  dried  soap  obtained  as  above,  is 
exhausted  with  petroleum  ether  of  low  boiling-point. 
The  petroleum  ether  is  then  evaporated  off  and  the 
residue  weighed  :  this  is  the  weight  of  the  fat  contained 
in  10  gm.  of  the  soap. 

(c)  Fatty  Acids. — The  residue  from  (b)  which  is  free 
from  fat  and  which  represents  10  gms.  of  the  soap,  is 
weighed   and  half  of   it  dissolved  in  water.     Normal 
nitric  acid  is  then  added  in  excess  to  liberate  the  fatty 
acids.     These  are  collected  on  a  tared  filter,  dried  and 
weighed.     This  weight  when  doubled  gives  the  amount 
of  fatty  acids  in  10  gms.  of  the  soap.     The  reaction  is 
illustrated  by  this  equation  : 

NaC18H3SO2  +  HNO3  =  HC18HS3O2  +  NaNO3. 

Sodium  oleate.  Oleic  acid- 

The  acid  filtrate  is  now  titrated  with  normal  soda  or 
potash,  using  phenolphthalein  as  an  indicator.  The 
difference  between  the  volumes  of  acid  and  alkali  solu- 
tions used  gives  roughly  the  quantity  of  total  alkali. 

(d)  Chlorides  and  Stilphatcs. — The   residual   neutral 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.      249 

liquid  from  the  above,  is  divided  into  two  equal  parts, 

N 
in  one  of  which  chlorine  is  estimated  by — AgNO3, 

using  potassium  chromate. 

In  the  other  sulphuric  acid  is  estimated  with  barium 
chloride. 

(e)  Free  Alkali,  (i.e.,  the  alkali  which  does  not  exist  as 
soap).— Ten  grammes  of  the  soap  are  dissolved  in  hot  al- 
cohol,and  one  drop  of  phenolphthalein  T.S.  added;  then 
carbonic-acid  gas  is  passed  through  the  solution  until 
the  color  disappears.  The  free  alkali  is  thus  converted 
into  sodium  carbonate,  which  is  insoluble  in  alcohol 
and  may  be  separated  by  filtration.  The  residue  on 
the  filter  is  washed  with  hot  alcohol,  and  then  dissolved 

N 

in  a  little  water  and  titrated  with  —  acid  in  the  pres- 
ence of  methyl-orange.  The  number  of  cc.  used  multi- 
plied by  0.0031  gives  the  grammes  of  free  alkali,  as 
Na2O,  in  the  10  gms.  of  soap. 

Combined  Alkali. — The  alcoholic  solution  from  the 
above  which  contains  the  combined  alkali  and  the  fatty 
acids,  is  diluted  with  a  little  water,  methyl-orange  added, 
and  the  mixture  titrated  with  decinormal  acid.  The 
quantity  of  combined  alkali  is  thus  found.  The  num- 
ber of  cc.  of  acid  consumed  multiplied  by  0.0031  gives 
the  quantity  as  NaaO. 

Another  Way  is  to  evaporate  the  alcoholic  solution  to 
dryness,  the  residue  then  ignited,  and  the  soap  thus 
converted  into  alkali  carbonate.  This  is  dissolved  in 
water  and  titrated  with  normal  or  decinormal  acid  in 
the  presence  of  methyl-orange. 

The  fatty  acids  are  found  by  using  the  factor  0.0282 
or  0.282.  The  number  of  cc.  of  decinormal  acid  used 


250      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

in  the  above  titration  when  multiplied  by  0.0282,  or  of 
normal  acid  when  multiplied  by  0.282,  gives  the  quan- 
tity of  fatty  acid  as  oleic.  Soaps,  however,  contain  var- 
ious fatty  acids  the  molecular  weights  of  which  differ. 

Therefore  in  estimating  the  fatty  acids  volumet- 
rically,  the  neutralizing  power  of  the  acids  liberated 
from  soap,  expressed  in  cc.  of  standard  alkali  and  called 
the  saponification  equivalent,  is  employed. 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS. 


CHAPTER   XX. 

DETERMINATION   OF   THE   MELTING-POINT   OF 
FATS. 

THE  melting-point  of  a  fat  can  be  quickly  found  by 
immersing  the  bulb  of  a  thermometer  in  the  melted 
fat,  then  suspending  the  bulb  which  is  coated  with  con- 
gealed fat  in  the  middle  of  a  beaker  of  water  to  which 
heat  is  gradually  applied,  and  noting  the  temperature 
at  which  the  fatty  coat  melts  from  the  bulb. 

Another  Way. — Draw  out  a  long  capillary  tube,  Fig.  26. 
Melt  the  fat,  and  draw  a  small  portion  of  it  up  into  the 
tube.  The  melted  fat  will  rise  in  the  tube  by 
capillary  attraction.  This  tube  is  bound  or  held 
against  the  bulb  of  a  thermometer,  and  im- 
mersed in  a  beaker  of  cold  water  to  which  heat 
is  applied.  The  fat  is  congealed  upon  immer- 
sion in  water  and  becomes  opaque.  When  the 
temperature  of  the  water  is  raised  to  the  proper 
degree,  the  opaque  cylinder  of  fat  melts  and  be- 
comes transparent.  At  this  point  the  tempera- 
ture must  be  noted.  The  congealing-point  may 
be  found  by  removing  the  source  of  heat  and 
allowing  the  water  to  cool  gradually,  and  noting  the 
point  at  which  the  fat  in  the  tube  again  congeals  and 
becomes  opaque.  The  congealing  may  be  hastened 
by  adding  cautiously  cold  water  to  that  in  the  beaker. 
The  congealing-point  will  be  identical  with,  or  close  to 
the  melting-point. 


252       A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 


CHAPTER   XXL 

ESTIMATION  OF  OIL  OR  FAT  IN  EMULSIONS  AND 
OINTMENTS. 

Apparatus. — A  test-tube  of  about  eight  inches   in 
length,  fitted   with  two  good   corks,  one  of  which  is 
provided   with  a  wash-bottle  arrange- 
ment, Fig.  27. 

The  Process. — A  weighed  quantity 
of  the  emulsion  (2  to  5  gms.)  or  ointment 
(l  to  2  gms.)  is  put  into  the  test-tube, 
the  latter  half  filled  with  ether,  corked 
and  shaken  for  about   5  minutes,  and 
set  aside  so  as  to  allow  the  liquids  to 
separate.     The  ethereal  solution  of  the 
fat  or  oil,  which  forms  the  upper  layer, 
is  carefully  drawn  off  into  a  tared  ves- 
sel.      This    is    done    by   inserting   the 
stopper  having  the  wash-bottle  arrange 
ment,  and  gently  blowing  in  the  tube 
a.    The  tube  b  is  raised  or  lowered  so 
that  its  lower  end  is  slightly  above  the 
surface  of  the  lower  layer  in  the  tube. 
This  process  is  repeated  until  the  fat  is  completely 
extracted,  which  is  shown  by  there  being  no  residue 
left,  when  a  few  drops  of  the  last  portion  drawn  off  are 
evaporated  on  a  watch-glass. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       253 


The  mixed  ethereal  solutions  are  now  subjected  to 
evaporation,    thus    leaving   the   oil 
behind.      The    tared    evaporating- 
dish  containing  the  oil  is  dried  in 
a  water-bath  and  weighed. 

By  deducting  the  weight  of  the 
dish  when  empty  from  the  above 
weight,  the  weight  of  the  fat  or  oil 
is  obtained. 

In  this  way  the  fat  in  powdered 
drugs,  in  chocolate,  in  milk,  etc., 
maybe  estimated.  The  estimation  is 
more  rapid  than  though  not  as  accu- 
rate as,  when  made  by  the  Soxhlet's 
extraction  apparatus  which  is  illus- 
trated in  Fig.  28.  Into  the  tarred 
flask  A  the  ether  or  other  solvent 
is  put.  The  substance  B,  inclosed 
in  a  cartridge  of  filtering-paper,  is 
introduced  into  the  tube  C.  The 
latter  in  turn  is  connected  with  an 
upright  condenser  D.  The  flask 
is  now  heated  by  a  water-bath,  and 
the  vapor  of  the  ether  rises  through 
E,  condenses  and  drops  onto  the 
powdered  substance  in  the  cartridge. 
When  the  instrument  has  become 
filled  by  the  solvent  to  the  level  of 
the  top  of  F,  it  runs  back  into  the 
flask  charged  with  part  of  the 
soluble  matter.  This  process  re- 
peats itself  until  the  whole  of  the  FlG-  28- 
soluble  matter  of  the  substance  has  been  extracted. 


254       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

The  flask  is  then  detached,  and  the  ether  evapo- 
rated or  distilled  off  ;  the  soluble  matter  of  the  origi- 
nal powder  being  left  in  the  flask.  Resinous  or  sticky 
substances  should  be  mixed  with  a  little  clean  sand,  in 
order  to  facilitate  the  extraction  and  prevent  clogging 
up  of  the  apparatus. 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.       255 


CHAPTER   XXII. 
ESTIMATION  OF  STARCH   IN  CEREALS,   ETC. 

THE  method  about  to  be  described  depends  upon 
the  fact  that  when  barium  hydroxide  is  brought  in 
contact  with  starch,  an  insoluble  compound  is  formed, 
the  formula  of  which  is  C24H40O20BaO.  This  combina- 
tion takes  place  in  definite  proportions,  so  that  if  an 
excess  of  barium  hydroxide  solution  is  added  to  the 
starchy  substance,  and  then  the  excess  estimated,  the 
quantity  which  combined  with  and  which  consequently 
represents  the  amount  of  starch  present,  is  found. 

Solutions  Required. — i.  Decinormal  Hydrochloric 
Acid.  See  page  40  (3.637  gm.  to  I  liter.)  Each  cc. 
represents  .00765  gm.  of  BaO. 

2.  Baryta-water  (barium  hydroxide  solution),  made 
by  dissolving  about  7  gms.  of  pure  crystallized  barium 
hydroxide  in  1000  cc.  of  water.  Should  be  kept  in  a 
special  vessel  such  as  is  illustrated  in  Fig.  23. 

The  Process. — The  sample  is  finely  powdered,  and 
I  gm.  weighed  out  for  analysis.  This  is  rubbed  up 
with  successive  portions  of  water  (using  not  more  than 
50  cc.)  and  transferred  to  a  flask  having  a  capacity  of 
about  150  cc.  The  flask  and  contents  are  now  heated 
upon  a  water-bath  for  half  an  hour  to  thoroughly 
gelatinize  the  starch.  If  the  substance  analyzed  con- 
tains oil,  this  must  first  be  extracted  in  a  "  Soxhlet'* 
apparatus  before  the  water  is  added. 


256      A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

If  free  starch  is  to  be  experimented  with,  0.2  or  0.3 
gm.  instead  of  I  gm.  should  be  taken. 

When  the  starch  is  gelatinized,  the  solution  is  cooled, 
and  25  cc.  of  the  baryta-water  are  added.  The  flask  is 
corked,  and  well  shaken  for  two  minutes;  proof  spirit  is 
then  added  to  make  about  125  cc.,  the  flask  again 
corked,  thoroughly  shaken,  and  set  aside  to  settle. 
While  settling  a  check  is  made  upon  10  cc.  of  the 
baryta-water  mixed  with  50  cc.  of  recently  boiled  dis- 
tilled water,  by  titrating  with  decinormal  hydrochloric 
acid,  using  phenolphtalein  as  indicator.  The  number 

N 
of  cc.  of  --  hydrochloric  acid  V.  S.  used,  is  noted,  and 

when  multiplied  by  2\  the  total  strength  of  the  25  cc. 
of  the  baryta-water  employed  in  the  analysis  is  ob- 
tained. 

When  the  settling  of  the  insoluble  compound  is 
completed,  25  cc.  of  the  clear  liquid  is  drawn  off  (this 
is  -^  of  the  entire  quantity)  with  a  pipette  and  rapidly 

N 
titrated  with  the  —  acid  V.  S.  in  the  presence  of  a  few 

10 

drops  of  phenolphtalein  T.  S.  The  number  of  cc. 
consumed  is  noted,  multiplied  by  5,  and  then  deducted 
from  the  number  representing  the  total  strength  of 
25  cc.  baryta-water.  The  difference  is  the  quantity 
which  went  into  combination  with  the  starch. 

N 
Each  cc.  of  the  —  hydrochloric  acid  V.  S.  represents 

0.00765  gm.  of  BaO3,  which  is  equivalent  to  0.0324  gm. 
of  starch. 

Therefore  by  multiplying  the  number  of  cc.  repre- 
senting the  quantity  of  baryta  which  combined  with 


A   TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS.       257 

the  starch  by  0.0324  gm.,  the  quantity  of  starch  pres- 
ent in  the  samph  is  obtained. 

Example.  —  I  gm.  of  substance  was  taken,  mixed  with 
50  cc.  of  water,  25  cc.  of  baryta-water,  and  sufficient 
proof  spirit  to  make  125  cc.  This  is  set  aside  and 
allowed  to  settle. 

The  reaction  which  takes  place  is  as  follows  : 

2C12H20010  +  BaO,HaO  =  C24  H40O3,BaO  +  H2O. 

Starch.  '  —  •  —  ' 

2)648  2)153.0 

324  76.5 

While  settling,  the  strength  of  the  baryta-water  is 
determined  by  titrating  with  decinormal  hydrochloric 
acid  V.  S.,  the  following  equation  being  applied  : 

BaO,H20  +  2HC1  =  BaCl2  +  2H3O. 

2)72.74 


_ 
*io)  76.5 


7.65  gms.  3.67  gms.  or  1000  cc.  —  V.  S. 

Thus  each  cc.  represents  0.00765  gm.  of  BaO. 

10  cc.  of  the  baryta-water  are  taken,  and  8  cc.  of  .the 

N 
-  acid  solution  are  required  to  neutralize  this.    There- 

fore 25  cc.  of  baryta-water  will  require  2  J  X  8  cc.  =  20 
cc.  of  ~  acid  V.  S. 

When  the  settling  is  completed,  25  cc.  of  the  clear 

N 

solution  is  drawn  off  and  titrated  with  —  acid  V.  S. 

10 

N 

We  will  assume  that  2.5  cc.  of  the  —  acid  V.  S.  are 

10 


258       A   TEXT-BOOK   OF   VOLUMETRIC    ANALYSTS. 

required  ;  therefore  the  entire  quantity  of  solution  will 
neutralize  5  X  2.5  cc.  =  12.5  cc. 

The  difference  between  12.5  cc.  and  20  cc.  =  7.5  cc., 

N 
which  is  the  loss  of  alkalinity  expressed  in  cc.  of  - 

N 
acid  V.  S.     Each  cc.  of  alkalinity  lost,  expressed  as  —  - 

acid  V.  S.,  indicates  that  0.00765  gm.  of  BaO  went  into 
combination  with  starch  ;  and  since  0.00765  gm.  of 
BaO  represents  0.0324  gm.  of  starch,  the  substance 
analyzed  contains  7.5  X  0.0324  gm.  or  0.243  gm.  of 
starch. 


Another  Method  for  Estimating  Starch  consists  in 
converting  it  into  glucose  and  then  estimating  the 
glucose  with  Fehling's  Solution. 

The  starch  is  weighed  and  boiled  in  a  flask  with 
water  containing  hydrochloric  acid  for  several  hours  ; 
the  solution  is  then  cooled,  neutralized  with  potassium 
hydroxide,  and  diluted  so  that  I  part  of  starch,  or 
rather  sugar,  shall  be  contained  in  200  parts  of  water. 
This  is  put  into  a  burette  and  titrated  into  10  cc.  of 
Fehling's  Solution,  as  described  below  under  Sugar. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       259 


CHAPTER   XXIII. 
ESTIMATION   OF   SUGARS. 

Fehling's  Solution. — (a)  The  Copper  Solution  — 
34.64  gms.  of  carefully  selected  small  crystals  of  pure 
cupric  sulphate  are  dissolved  in  sufficient  water  to 
make,  at  or  near  15°  C.  (59°  F.),  exactly  500  cc.  Keep 
in  small  well-stoppered  bottles. 

(b)  The  Alkaline-tartrate  Solution. — 173  gms.  of  po- 
tassium and  sodium  tartrate  (Rochelle  salt)  and  125 
gms.  of  potassium  hydroxide,  U.  S.  P.,  are  dissolved  in 
sufficient  water  to  make,  at  or  near  15°  C.  (59°  F.),  ex- 
actly 500  cc.  Keep  in  small  rubber-stoppered  bottles. 

For  use,  equal  quantities  of  the  two  solutions  should 
be  mixed  at  the  time  required. 

IO  cc.  of  the  mixed  solution  is  equivalent  to 

Glucose 050 

Maltose 082 

Inverted  cane-sugar 0475 

Inverted  starch 045 

The  Process. — 0.5  gm.  or  less  of  the  sugar  is  dis- 
solved in  100  cc.  of  water.  This  liquid  is  placed  in  a 
burette.  10  cc.  of  the  Fehling's  Solution  are  mixed 
with  50  cc.  of  water  and  placed  in  a  porcelain  dish  over 
a  Bunsen  burner  and  heated  to  boiling.  The  sugar 
solution  is  then  run  in  from  the  burette,  until  all  blue 
color  is  destroyed. 


260      A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

It  is  always  somewhat  difficult  to  determine  the 
exact  point  at  which  the  blue  color  disappears,  owing 
to  the  presence  of  the  precipitated  suboxide  of  copper. 
This  difficulty  may  be  overcome  by  the  addition  of 
some  substance  which  will  prevent  the  precipitation  of 
the  cuprous  oxide,  such  as  ammonium  hydroxide  or 
potassium  ferrocyanide.  The  disappearance  of  the 
blue  color  can  then  be  readily  seen,  as  the  solution  re- 
mains clear  to  the  end,  turning  from  blue  to  green,  and 
finally  brown,  which  indicates  the  end  of  the  reaction. 

Professor  Hartley  reports  this  method  as  accurate, 
reliable,  and  rapid,  provided  the  solution  be  not  boiled 
during  the  reduction.  He  recommends  to  add  to  the 
Fehling's  Solution  in  the  porcelain  basin  10  cc.  of  a 
10$  freshly  prepared  solution  of  potassium  ferrocy- 
anide and  30  cc.  of  water.  The  ferrocyanide  does  not 
precipitate  the  copper  in  alkaline  solution. 

If  the  sugar  to  be  examined  be  either  glucose,  malt- 
ose, or  lactose,  it  may  be  titrated  directly;  but  if  it  be 
cane-sugar,  it  must  first  be  inverted.  This  is  done  by 
dissolving  the  sugar  (0.475  gm.)  in  about  100  cc.  of 
water,  adding  3  or  4  drops  of  strong  hydrochloric  acid, 
and  boiling  briskly  for  ten  or  fifteen  minutes.  This  is 
then  allowed  to  cool,  neutralized  with  potassium  hy- 
droxide, and  made  up  to  100  cc.  with  water. 

The  Calculation. — 10  cc.  of  Fehling's  Solution  are 
always  taken  ;  and  whatever  the  quantity  of  glucose 
or  sugar  solution  is  required  to  effect  reduction,  that 
quantity  contains  the  equivalent  of  10  cc.  of  Fehling's 
Solution.  Thus  if  12  cc.  of  the  sugar  solution  were 
required  to  reduce  10  cc.  of  Fehling's  Solution,  the  12 
cc.  contain  0.05  gm.  of  glucose  or  0.082  gm.  of  maltose, 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       261 

etc.     100  cc.  of  the  solution  therefore  contain  x  gm.  of 
glucose. 

.05  x  ioo 


12 


=  0.416  gm.  glucose. 


The  sugar  in  urine  may  be  estimated  by  this  process. 
The  urine  is  placed  in  the  burette  and  run  into  the 
boiling  Fehling's  Solution  in  the  usual  manner.  If  it 
contain  a  large  quantity  of  sugar,  it  must  be  diluted 
two  or  three  times. 

In  estimating  with  Fehling's  Solution  it  is  well  to 
attach  a  rubber  tube  8  to  12  inches  in  length  to  the 
lower  end  of  the  burette,  so  that  the  boiling  need  not 
be  done  directly  under  the  burette,  and  thus  cause  in- 
correct readings  through  the  expansion  of  the  liquid 
therein. 


262       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


CHAPTER   XXIV. 


ESTIMATION  OF  GLYCERIN. 

Glycerin     (Glycerol)    C3H5(OH)3  =  j  ^-79  __The 

estimation  of  glycerin,  of  fats,  etc.,  may  be  made  by 
the  method  of  Benedikt  and  Zsigmondy.  This  method 
consists  in  saponifying  the  fat  and  oxidizing  the  result- 
ant glycerin  by  permanganate  in  alkaline  solution  ;  thus 
oxalic  acid,  carbon  dioxide,  and  water  are  formed  The 
excess  of  permanganate  is  then  destroyed  by  sulphurous 
acid  or  a  sulphite,  the  liquid  filtered  to  separate  the 
manganese  dioxide,  and  the  oxalic  acid  then  precipi- 
tated by  a  soluble  calcium  salt  in  the  presence  of  acetic 
acid,  and  the  precipitated  calcium  oxalate  then  titrated 
with  permanganate,  or  after  ignition  and  conversion 
into  carbonate  titrated  with  standard  acid  solution  in 
the  usual  way. 

Aqueous  solutions  of  glycerin  may  of  course  be  sub- 
mitted to  the  method  very  easily. 

The  reactions  are  as  follows  : 


C8H5(OH)8  +  2KMn04  =  K2C2O4 

92  (Potassium 

oxalate) 
1  66 


then 

K2C2O4  +  CaCl3  =  2KC1  +  CaC2O4  ; 

166  (Calcium  oxalate) 

128 


A  TEXT-BOOK  OF    VOLUMETRIC   ANALYSIS.       263 
then 

5CaC2O4  +  8H2SO4  +  2KMnO4  =  sCaSO, 
100)640  100)315  N 

6.40  gms.  3.15  gms.  or  1000  cc.  —  V.  S. 

10 

-f  2MnSO4  +  K2S04  +  8H20  +  ioCO3. 

N 
Thus  1000  cc.  —   permanganate  solution  represents 

6.4  gms.  of  calcium  oxalate,  which  is  equivalent  to  8.3 
gms.  of  potassium  oxalate,  which  is  equivalent  to  4.6 
gms.  of  glycerin. 

Thus  each  cc.  of  the  permanganate  solution  of  deci- 
normal  strength  used  up  by  the  calcium  oxalate  repre- 
sents .0046  gm.  of  glycerin. 

If  the  precipitated  calcium  oxalate  is  ignited  and 
converted  into  carbonate,  and  the  carbonate  then 
titrated  with  decinormal  sulphuric  or  hydrochloric 
acid,  the  reactions  are  as  follows  : 


+  O2  =  2CaCO3  +  2CO2  ; 
4)256  4)200 

10)  64  io)  SQ_ 

6.4  gms.  5.0  gms. 

2CaCO3  +  2H2SO4  =  2CaSO4  +  2H2O  +  2COa. 
4)200  4)196 

io)  5Q  io)  49  N 

5.0  gms.  4.9  gms.  or  1000  cc.  —  V.  S. 

io 

Thus  each  cc.  of  decinormal  acid  represents  0.005  gm- 
of  CaCO3,  or  0.0064  gm.  of  calcium  oxalate,  or  .0046 
gm.  of  glycerin. 

If  experimenting  with  pure  glycerin,  operate  upon  io 
cc.  of  a  2%  solution.  This  is  diluted  with  cold  water 


264      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

to  about  400  cc.,  about  10  gms.  of  caustic  potash  are 
added  to  this,  and  then  a  saturated  solution  of  potas- 
sium permanganate  until  the  liquid  is  no  longer  green, 
but  blue  or  blackish.  An  excess  does  no  harm. 

The  liquid  is  then  boiled  for  about  one  hour,  and  a 
strong  solution  of  sodium  sulphite  is  added  to  the 
boiling  liquid  until  the  violet  or  green  color  is  de- 
stroyed ;  the  liquid  is  then  filtered  while  yet  hot,  to  sepa- 
rate the  precipitated  manganese  dioxide.  When  cool, 
it  is  acidified  with  acetic  acid,  and  calcium  chloride 
added  to  precipitate  the  oxalic  acid  as  calcium  oxalate. 
When  the  deposition  of  calcium  oxalate  is  complete  it 
is  separated  by  filtration,  and  titrated  either  with  per- 
manganate or  after  ignition  with  standard  sulphuric 
acid. 

The  former  method  is  preferable.  For  this  purpose 
the  filter  is  pierced,  and  the  precipitate  rinsed  into  a 
porcelain  basin  ;  about  10  cc.  of  dilute  sulphuric  acid 
are  then  added  through  the  funnel  slowly,  so  that  it 
comes  into  contact  with  and  washes  through  any  of 
the  precipitate  that  may  still  cling  to  it. 

The  liquid  is  now  diluted  to  about  200  cc.,  brought 
to  60°  C.,  and  the  decinormal  permanganate  run  in 
from  a  burette,  slowly,  until  a  faint  but  distinct  pink 
color  appears  and  remains  permanent  after  stirring; 
each  cc.  of  the  permanganate  thus  used  represents 
0.0046  gm.  of  glycerin. 

The  process  for  estimating  the  glycerin  of  fats  is  as 
follows : 

Ten  grammes  of  the  fat  or  oil  are  placed  in  a  strong 
small  bottle  together  with  4  gms.  of  pure  potassium 
hydroxide,  dissolved  in  25  cc.  of  water;  the  bottle  is 
then  closed  with  a  solid  rubber  stopper  and  tied  down 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       26$ 

firmly  with  wire ;  it  is  then  placed  in  boiling  water  and 
heated,  with  occasional  shaking,  from  six  to  ten  hours, 
or  until  the  fat  or  oil  is  completely  saponified.  The 
contents  of  the  bottle  are  then  poured  into  a  beaker 
and  diluted  with  hot  water;  this  should  give  a  clear 
solution. 

A  dilute  acid  is  then  added  to  separate  the  fatty 
acids,  which  are  filtered  out  and  the  filtrate  made  up 
to  a  given  volume. 

This  solution,  which  will  usually  contain  0.2  to  0.5 
gm.  of  glycerin,  according  to  its  origin,  is  transferred 
to  a  porcelain  basin,  diluted  with  cold  water  to  about 
400  cc.,  and  the  glycerin  estimated  as  described  under 
the  experiment  with  pure  glycerin. 


266      A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


CHAPTER    XXV. 
ESTIMATION   OF   PHENOL. 

Decinormal  Bromine,  V.  S.  (Koppeschaar's  Solu- 
tion),  Br  =  {  4976  ^.976  J  gms_  in 


KBr       —  118.79  NaBr       =  102.76 

KBrO3  =  166.67  NaBrO3  =  150.64 

This  solution  does  not  contain  free  bromine,  but  it 
contains  two  salts,  a  bromide  and  a  bromate,  which 
when  treated  with  hydrochloric  acid,  liberate  a  definite 
quantity  of  bromine. 

It  is  made  as  follows  : 

Dissolve  3  gms.  of  sodium  bromate  and  50  gms.  of 
sodium  bromide  (or  3.2  gms.  of  potassium  bromate  and 
50  gms.  of  potassium  bromide)  in  sufficient  water  to 
make  900  cc. 

Transfer  20  cc.  of  this  solution  by  means  of  a  pipette 
into  a  bottle  having  a  capacity  of  about  250  cc.,  pro- 
vided with  a  glass  stopper  ;  add  75  cc.  of  water,  then  5 
cc.  of  pure  hydrochloric  acid,  and  immediately  insert 
the  stopper. 

Shake  the  bottle  a  few  times,  then  remove  the 
stopper  just  sufficiently  to  quickly  introduce  5  cc.  of 
potassium  iodide  T.  S.,  taking  care  that  no  bromine 
vapor  escape,  and  immediately  stopper  the  bottle. 

Agitate  the  bottle  thoroughly,  remove  the  stopper 
and  rinse  it  and  the  neck  of  the  bottle  with  a  little 
water  so  that  the  washings  flow  into  the  bottle,  then 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.       267 

add  from  a  burette  decinormal  sodium  thiosulphate 
V.  S.  until  the  color  of  the  free  iodine  is  nearly  all  dis- 
charged, then  add  a  few  drops  of  starch  T.  S.,  and  con- 

N 
tinue  the  titration  with  —  thiosulphate  V.  S.  until  the 

blue  color  disappears. 

N 

Note  the  number  of  cc.  of  the  —  sodium  thiosul- 

10 

phate  V.  S.  thus  used,  and  dilute  the  bromine  solution 

N 

so  that  equal  volumes  of  it  and  the  —  sodium  thiosul- 

10 

phate  V.  S.  will  exactly  correspond  to  each  other  under 
the  above-mentioned  conditions. 

Example. — Assuming   that   the    20   cc.   of   bromine 

N 
solution   required   25.2   cc.  of  the   —   thiosulphate  to 

completely  absorb  the  iodine,  the  bromine  solution 
must  be  diluted  in  the  proportion  of  20  to  2.5.2  ;  that 
is,  each  20  cc.  must  be  diluted  to  make  25.2  cc. 

Thus  if  850  cc.  are  left,  they  must  be  diluted  to 
make  1071  cc.,  and  the  solution  is  decinormal. 

A  new  trial  should  always  be  made  after  diluting, 
and  the  bromine  solution  should  correspond,  volume 
for  volume,  with  the  decinormal  sodium  thiosulphate 
V.  S. 

The  first  step  in  the  preparation  of  this  solution  is 
to  dissolve  the  salts  ;  then  hydrochloric  acid  is  added, 
which  liberates  a  definite  quantity  of  bromine,  as  the 
equation  illustrates  : 

SNaBr  +  NaBrO3  +  6HC1  =  6NaCl  +  sBr,  +  3H3O. 

The  stopper  should  be  inserted  into  the  bottle  as 
soon  as  the  hydrochloric  acid  has  been  added,  in  order 


268      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

that  no  bromine  vapor  escape,  and  the  bottle  rotated 
so  as  to  mix  the  acid  thoroughly  with  the  liquid. 

The  next  step  is  to  determine  the  quantity  of  bro- 
mine which  a  definite  volume  of  solution  will  liberate. 
The  bromine  solution  should  be  of  such  strength  that 
1000  cc.  of  it  will  contain  7.976  gms.  of  available  bro- 
mine. Bromine,  like  chlorine,  liberates  iodine  from 
potassium  iodide,  and  is  estimated  in  the  same  man- 
ner. 

One  atomic  weight  of  iodine  is  liberated  by  one 
atomic  weight  of  bromine: 

Br2  +  2KI  =  2KBr  +  I2. 

Thus  by  determining  the  quantity  of  iodine  liber- 
ated the  quantity  of  bromine  is  found. 

N 

The  iodine  is  determined  by  the  —  sodium  thiosul- 

10 

phate  V.  S.,  one  litre  of  which  represents  12.65  gms.  of 
iodine,  which  is  equivalent  to  7.976  gms.  of  bromine,  as 
is  shown  by  the  following  equation  : 

(Br.)       =       I,+  2(Na2S203  +  5H20) 
20)159-52          20)253  20)496  N 

7.976  gms.        12.65  gms.  24.8  gms.  or  1000  cc.  —  V.  S. 

=  2NaI  +  Na2S406  +  ioH2O. 

Carbolic  Acid,  C6HB(OH)  =  j  ^378  (Phenol)  Phe, 

nylhydrate,  Hydroxylbenzene,  Phenylalcohol). — This 
is  regarded  as  benzene  (C6H6)  in  which  one  atom  of 
hydrogen  has  been  replaced  by  hydroxyl  (OH). 

The  Valuation  of  Carbolic  Acid  according  to  the 
U.  S.  P.  is  as  follows  : 

1.563  gm.  of  the  carbolic  acid  are  dissolved  in  sum"- 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       269 

cient  water  to  make  1000  cc.  25  cc.  of  this  solution, 
containing  0.039  gm.  of  the  acid,  are  transferred  to 
a  glass-stoppered  bottle  having  a  capacity  of  about 
200  cc. 

To  this  30  cc.  of  decinormal  bromine  V.  S.,  followed 
by  5  cc.  of  hydrochloric  acid,  are  added,  and  the  bottle 
immediately  stoppered,  and  shaken  repeatedly  during 
half  an  hour. 

Then  the  stopper  is  removed  just  sufficiently  to 
introduce  5  cc.  of  a  20 -per -cent,  aqueous  solution 
of  potassium  iodide,  being  careful  that  no  bromine 
escape. 

The  bottle  is  then  thoroughly  shaken  and  the  neck 
rinsed  with  a  little  water,  the  washings  being  allowed 
to  flow  into  the  bottle. 

The  solution  is  now  ready  for  titration,  and  the 
decinormal  sodium  thiosulphate  is  delivered  in  from  a 
burette,  until  the  iodine  is  almost  completely  absorbed  ; 
then  add  a  few  drops  of  starch  T.  S.,  and  continue  the 
titration  until  the  blue  color  is  just  discharged. 

N 
Note   the   number  of  cc.   of    —  thiosulphate  V.  S. 

used ;  deduct  this  number  from  30  cc.  (the  quantity  of 

N 
-  bromine  V.  S.  originally  added),  and  the  quantity 

N 

of  --  bromine  V.  S.  which  went  into  combination  with 
10 

the  phenol  is  obtained. 
I 

Each  cc.  of  - 
H 

of  pure  phenol. 

N 
Example. — Assuming  that  6  cc.  of  —  sodium  thio- 


N 
Each  cc.  of  —  bromine  V.  S.  represents  0.001563  gm. 


270      A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

sulphate  were  required  to  discharge  the  color  of  the 
starch  iodide,  this  deducted  from  30  cc.  leaves  24  cc., 
the  quantity  which  combined  with  the  phenol. 

0.001563  X  24  =  .037512  gm. 

0.037512  X  ioo         f.     .     , 

-  =  96.  i #  of  pure  phenol. 
0.039 

The  above  method  originated  with  Koppeschaar, 
and  is  the  only  volumetric  method  by  which  accurate 
results  may  be  obtained. 

It  is  based  upon  the  fact  that  bromine  reacts  with 
phenol,  producing  an  insoluble  precipitate  of  tribrom- 
phenol. 

The  titration  is  not  made  directly ;  but  the  phenol 
solution  is  treated  with  an  excess  of  standard  bromine 
solution  in  the  presence  of  some  hydrochloric  acid. 
The  hydrochloric  acid  liberates  the  bromine,  and  the 
freed  bromine  then  reacts  with  the  phenol,  as  shown 
by  the  equations  : 

(a)  5NaBr  +  NaBrO3+6HCl=:6NaCl  +  3HaO+3Br2; 

(b)  C6H6OH    +   3Br2  =  C6H2Br3OH  +  3HBr. 

6)93.78  6)478.56 

10)15.63  10)  79-76  N 

1.563  gms.          7.976  gms.  or  1000  cc.  —  bromine  V.  S. 

N 
Thus  each  cc.  of  the  —   bromine  V.  S.  represents 

0.001563  gm.  of  pure  phenol. 

The  bromine  solution  which  was  added  in  excess, 
and  the  liberated  bromine  of  which,  is  not  fixed  by 

N 
phenol,  is   then   found   by   residual  titration   with   - 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       271 

sodium  thiosulphate  V.  S.  after  the  addition  of  some 
potassium  iodide. 

The  decinormal  bromine  solution  and  the  decinor- 
mal  sodium  thiosulphate  solution  being  equivalent, 
each  cc.  of  the  latter  consumed  represents  one  cc.  of 
the  former.  Then  by  subtracting  the  number  of  cc.  of 
the  sodium  thiosulphate  solution  used  from  the  num- 
ber of  cc.  of  bromine  solution  originally  added,  the 
quantity  of  the  latter  which  was  actually  consumed  by 
the  phenol  present  is  found.  This  number  when  mul- 
tiplied by  the  factor  for  phenol  then  gives  the  quantity 
of  pure  phenol  present. 

The  hydrochloric  acid  used  in  the  above  estimation 
must  contain  no  free  chlorine.  The  potassium  iodide 
must  be  free  from  iodate.  The  starch  T.S.  should  not 
be  added  until  most  of  the  free  iodine  has  been  taken 
up,  and  the  color  of  the  solution  has  diminished  to  light 
yellow. 

The  carbolic  acid  should  be  diluted  with  water  be- 
fore titration,  and  should  never  be  stronger  than  o.i 
gm.  in  25  cc. 

Mr.  H.  Bechurts  reports  that  the  precipitate  obtained 
from  phenol  and  bromine  is  not  pure  tribromphenol, 
but  a  mixture  of  tribromphenol  (C6H2Br3OH)  and  tri- 
bromphenol bromide  (C6H2Br3OBr). 

Thus  the  results  obtained  by  direct  titration  are 
often  too  high,  since  in  the  formation  of  tribromphenol 
only  6  atoms  of  bromine  are  required,  while  for  the 
production  of  tribromphenol  bromide  8  atoms  of  bro- 
mine are  taken  up  by  one  molecule  of  phenol. 

The  correct  results  obtained  by  Koppeschaar's 
method  are  attributable. to  the  use  of  potassium  iodide, 


272       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

which  decomposes  the  tribromphenol  bromide,  liberat- 
ing iodine,  thus : 

C.H3Br3OBr  +  2KI  =  C6H3Br3OK  +  KBr  +  I,. 

The  free  iodine  is  then  estimated  by  residual  titra- 
tion,  together  with  that  liberated  by  the  excess  of  bro- 
mine added. 

Thus  the  nature  of  the  original  precipitate  does  not 
affect  the  final  results. 


ESTIMATION   OF  PHENOL  BY  DR.   WALLER'S    METHOD. 

Solutions  Required. — i.  A  standard  solution  of 
phenol  containing  10  gms.  of  pure  phenol  in  I  litre. 

2.  Diluted  sulphuric  acid  of  15$  or  20$  strength,  sat- 
urated with  alum.     This  is  needed  to  facilitate  the  set- 
tling of  the  precipitate. 

3.  A  solution  of  bromine  in  water. 

The  Estimation. — Of  the  sample  10  gms.  are  in- 
troduced into  a  litre  flask,  and  made  up  with  water  to 
one  litre.  This  solution  is  filtered  through  a  dry  filter^ 
and  10  cc.  of  the  clear  filtrate  taken  for  analysis.  It  is 
placed  into  an  8-oz.  glass-stoppered  bottle,  and  about 
30  cc.  of  the  acid-alum  solution  added.  Into  another 
bottle  of  the  same  kind  10  cc.  of  the  standard  phenol 
solution  is  put,  and  to  this  also  30  cc.  of  the  acid-alum 
solution  are  added. 

The  bromine  solution  is  now  added  from  a  burette 
to  the  bottle  containing  the  standard  phenol  solution 
till  no  more  precipitate  forms,  the  bottle  being  stop- 
pered and  well  shaken  after  each  addition.  The  end 
reaction  is  further  indicated  by  the  appearance  of  a 


A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       2/3 

yellow  color  when  a  slight  excess  of  bromine  is  reached. 
Near  the  end  the  precipitate  forms  slowly. 

The  other  solution  containing  the  sample  under 
analysis  is  titrated  in  the  same  way.  Then  the  calcu- 
lation is  made  as  follows  : 

The  number  of  cc.  of  bromine  solution  consumed  by 
the  sample  is  multiplied  by  100,  and  then  divided  by 
the  number  of  cc.  of  bromine  solution  used  by  the 
standard  phenol  solution.  The  answer  is  the  per  cent, 
of  pure  phenol  contained  in  the  sample  analyzed. 

The  Amount  of  Water  contained  in  a  solution  of 
carbolic  acid  may  be  determined  by  agitating  the  so- 
lution with  an  equal  volume  of  chloroform  in  a  gradu- 
ated cylinder.  After  standing,  the  upper  layer  consists 
of  the  water  contained  in  the  mixture. 

Crude  or  Impure  Carbolic  Acid. — Phenol  in  crude 
carbolic  acid  is  estimated  after  separating  the  tarry 
matters.  20  cc.  of  the  crude  carbolic  acid  are  placed 
in  a  beaker  with  20  cc.  of  a  strong  solution  of  potas- 
sium hydrate  (sp.  gr.  about  1.30).  The  mixture  is  well 
shaken  and  allowed  to  stand  for  half  an  hour;  it  is  then 
diluted  to  J  litre  with  water.  The  tarry  matters  and 
other  foreign  impurities  are  thus  set  free,  and  may  be 
removed  by  filtration,  the  filter  and  contents  being 
washed  with  lukewarm  water  till  the  washings  are  no 
longer  alkaline.  The  filtrate  and  washings  are  then 
slightly  acidulated  with  hydrochloric  acid,  and  made 
up  to  3  litres  with  water. 

The  small  quantity  of  tarry  matters  which  is  left  in 
the  filtrate  does  not  interfere  in  the  titration  which 
follows.  50  cc.  of  this  solution  are  now  taken,  and 
1 20  cc.  of  the  decinormal  bromine  V.  S.  are  added, 
followed  by  5  cc.  of  hydrochloric  acid,  and  the  mixture 


2/4       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

shaken  frequently  during  half  an  hour.  10  cc.  of  po- 
tassium iodide  T.  S.  are  then  added,  shaken,  allowed 
to  rest  (not  longer  than  5  minutes),  and  finally  titrated 
with  decinormal  sodium  thiosulphate,  using  starch  T.  S. 
as  an  indicator. 

The  number  of  cc.  of  the  thiosulphate  solution  used 

N 

are  deducted  from  120  cc.,  the  quantity  of — bro- 
mine V.  S.  originally  added,  and  the  quantity  of  the 
latter  which  was  actually  taken  up  by  the  phenol 
is  obtained.  This  figure  when  multiplied  by  the  factor 
for  phenol,  0.001563  gm.,  gives  the  quantity  of  phenol 
present  in  the  sample  operated  upon.  It  must  be  re- 
membered that  the  50  cc.  of  the  diluted  carbolic  acid 
used  in  this  assay  represent  -J  of  one  cc.  of  the  original 
sample. 

Example. — Let  us  assume  that  80  cc.  of  decinormal 
sodium  thiosulphate  were  required  in  the  residual  titra- 
tion.  Deducting  this  from  120  leaves  40  cc.  of  bro- 
mine V.  S.  which  actually  went  into  combination  with 
the  phenol ;  then  40  X  .001563  =  0.06252  gm.  of  phenol 
present  in  0.33  cc.  of  the  solution  analyzed. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       2/5 


CHAPTER  XXVI. 
PEPSIN. 

PEPSIN,  the  active  constituent  of  the  gastric  juice,  is 
an  albuminous  principle  secreted  by  glands  imbedded 
in  the  lining  membrane  of  the  stomach. 

Pepsin  has  never  been  isolated  in  a  pure  state,  and 
its  exact  chemical  composition  is  not  known,  therefore 
pepsin  cannot  be  quantitatively  estimated ;  but  the 
digestive  strength  of  pepsin  or  its  preparations  is  meas- 
ured by  the  amount  of  egg-albumen  it  will  digest 
under  certain  conditions. 

A  good  pepsin  should  digest  2000  times  its  own 
weight  of  albumen. 

The  different  tests  for  ascertaining  the  digestive 
power  of  pepsin  do  not  give  the  actual  strength,  but 
serve  to  show  whether  a  sample  is  above,  below,  or 
near  the  standard.  All  the  known  tests  are  compara- 
tive tests,  and  must  be  conducted  under  like  conditions, 
as  slight  variations  in  the  manipulation  will  frequently 
occasion  very  different  results  even  with  the  same 
pepsin. 

In  testing  pepsin,  it  is  generally  assumed  that  the 
sample  which  will  so  change  the  largest  amount  of  egg- 
albumen  as  to  render  it  soluble  is  the  best. 

Coagulated  egg-albumen  is  not  readily  soluble,  but 
when  acted  upon  by  pepsin  it  is  converted  into  a  sub- 
stance  which  is  soluble. 


2/6       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

The  value  of  pepsin  as  a  digestive  agent  does  not, 
however,  lie  in  its  power  to  convert  albumen  into  a 
soluble  substance,  but  rather  in  the  amount  of  a  certain 
soluble  and  diffusible  principle  (peptone)  which  it  pro- 
duces in  a  given  time  and  under  certain  conditions. 

The  function  of  the  gastric  juice  in  the  animal  econ- 
omy consists  in  reducing  the  proteids  of  the  food  to  a 
condition  in  which  they  are  easily  absorbed  into  the 
system,  and  not  reducing  them  to  a  soluble  condition. 

This  conversion  of  the  indiffusible  proteids  into  solu- 
ble and  diffusible  peptone  does  not  take  place  at  once, 
but  occurs  only  after  they  have  passed  through  several 
successive  stages. 

The  first  step  in  the  digestive  action  of  pepsin  upon 
coagulated  egg-albumen  is  the  conversion  of  the  latter 
into  soluble  acid-albumen,  or  syntonin,  from  which 
state  it  is  subsequently  converted  into  parapeptone, 
metapeptene,  and  finally  peptone. 

The  latter  is  the  only  one  of  these  products  which  is 
highly  diffusible,  hence  the  albumen  is  not  digested 
until  it  is  converted  into  peptone. 

Thus  it  is  seen  that  in  the  tests  in  which  the  dissolv- 
ing power  of  a  pepsin  is  alone  taken  into  account  the 
actual  digestive  power  is  not  ascertained. 

A  weak  pepsin  may  dissolve  a  large  quantity  of  albu- 
men and  convert  it  into  syntonin,  but  will  carry  the 
digestion  no  further,  while  a  stronger  pepsin  may  in 
the  same  time  convert  the  same  amount  of  albumen 
not  only  into  syntonin,  but  also  into  peptone.  Ap- 
parently both  samples  have  done  equal  work,  the 
albumen  being  dissolved  in  both  cases,  while  in  reality 
one  is  double  the  strength  of  the  other. 

When  pepsin  is  brought  in  contact  with  more  albu- 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.      277 

men  than  it  can  thoroughly  digest,  the  latter  is  con- 
verted principally  into  syntonin,  and  little  or  no  pep- 
tone is  formed  ;  thus  in  order  to  determine  the  real 
digestive  power  of  a  pepsin,  it  is  necessary  to  find  out 
how  much  peptone  it  produces  in  a  certain  period. 

This  may  be  accomplished  by  boiling  the  solution 
when  the  time  is  up,  to  prevent  further  action  of  the 
pepsin  ;  the  solution  is  then  filtered  while  still  hot,  and 
neutralized  with  sodium  carbonate  ;  the  syntonin  will 
then  be  precipitated. 

This  precipitate  should  be  dried  to  a  constant  weight, 
and  weighed  ;  the  difference  between  this  weight  and 
the  weight  of  the  albumen  originally  taken  will  give 
approximately  the  quantity  of  peptone  produced.  If, 
however,  the  albumen  was  not  completely  dissolved, 
that  remaining  must  also  be  deducted  from  the  quan- 
tity first  taken. 

It  must  not  be  forgotten  that  the  conditions  of  tem- 
perature, acidity,  time,  amount  of  agitation,  etc.,  must 
be  the  same  in  all  cases. 

The  U.  S.  P.  method  for  the  valuation  of  pepsin  is 
as  follows : 

Solutions  Required. — (a)  To  294  cc.  of  water  add 
6  cc.  of  diluted  hydrochloric  acid. 

(b)  In  100  cc.  of  solution  (a)  dissolve  0.067  gm.  (i  gr.) 
of  the  pepsin  to  be  tested. 

(c)  To  95  cc.  of  solution  (a)  brought  to  a  temperature 
of  40°  C.  (104°  F.)  add  5  cc.  of  solution  (b}. 

The  resulting  100  cc.  of  liquid  will  contain  0.21  gm. 
(0.2  cc.)  of  absolute  hydrochloric  acid,  0.00335  gm-  °f 
the  pepsin  to  be  tested,  and  98  cc.  of  water. 

Immerse  and  keep  a  fresh  hen's  egg  for  fifteen  min- 
utes in  boiling  water.  Then  remove  it  and  place  in 


2;8       A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

cold  water.  When  it  is  cold,  separate  the  white,  coag- 
ulated albumen,  and  rub  it  through  a  clean  sieve 
having  30  meshes  to  the  linear  inch.  Reject  the  first 
portion  passing  through  the  sieve.  Weigh  off  10  gms. 
of  the  second  clean  portion,  place  in  a  flask  of  about 
200  cc.  capacity,  and  add  one  half  of  solution  (c),  and 
shake  to  distribute  the  albumen  evenly  through  the 
liquid.  Then  add  the  other  half  of  solution  (c)  and  shake. 
Place  the  flask  on  a  water-bath  and  keep  the  temperature 
at  about  40°  C.  (104°  F.)  for  six  hours,  shaking  gently 
every  fifteen  minutes.  At  the  expiration  of  this  time 
the  albumen  should  have  disappeared,  leaving  at  most 
only  a  few  thin,  insoluble  flakes.  The  U.  S.  P.  re- 
quirement is  that  the  pepsin  should  be  capable  of 
digesting  (dissolving)  3000  times  its  own  weight  of  egg- 
albumen,  coagulated  and  disintegrated  as  described 
above. 

The  relative  proteolytic  power  of  pepsin  stronger  or 
weaker  than  that  above  described  may  be  determined 
by  ascertaining  how  much  of  solution  (ft)  made  up  to 
TOO  cc.  with  solution  (a)  will  be  required  to  exactly 
dissolve  10  gms.  of  coagulated  and  disintegrated  albu- 
men under  the  conditions  given  above. 

This  method  is  somewhat  cumbersome  and  tedious. 

The  following  is  Professor  Hartley's  favorite  method. 
In  the  hands  of  the  author  it  has  given  entirely  satis- 
factory results. 

Solutions  Required. — (a)  To  25  gms.  of  the  well- 
mixed  whites  of  several  eggs  add  enough  distilled 
water  to  make  exactly  250  cc.  Mix  well  by  thor- 
oughly shaking  with  clean  fine  gravel,  and  boil  for  5 
minutes.  After  cooling,  make  up  the  solution  to  the 
original  volume  with  water.  This  solution  contains 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS. 

about  10$  of  egg-albumen,  or  about  1.22  gms.  of  the 
dry  albumen  in  100  cc. 

(&)  One  gm.  of  the  pepsin  to  be  tested  is  dissolved 
in  25  cc.  of  water.  2  cc.  of  diluted  hydrochloric  acid 
(U.  S.  P.)  are  added,  and  enough  water  to  bring  the 
solution  up  to  50  cc. 

Procedure. — Measure  out  into  a  beaker  or  bottle  50 
cc,  of  the  albumen  solution,  and  warm  on  a  water-bath 
to  about  40°  C.  (104°  F.).  Add  to  this  2  cc.  of  diluted 
hydrochloric  acid,  and  from  0.5  to  5.0  cc.  of  the  pepsin 
solution.  The  more  active  the  pepsin  the  less  the 
quantity  of  the  pepsin  solution  is  to  be  taken.  It  is 
sometimes  necessary  with  a  pepsin  of  unknown  strength 
to  make  a  preliminary  test,  to  determine  the  approxi- 
mate time  required  by  the  digestion,  as  it  is  best  to  so 
regulate  the  quantity  of  pepsin  and  albumen  that  the 
digestion  shall  be  complete  in  two  hours  or  less.  The 
time  when  the  pepsin  is  added  must  be  carefully  noted, 
and  the  temperature  kept  at  about  35°  to  40°  C.  (95°  to 
104°  F.).  At  intervals  of  10  minutes  a  few  drops  of  the 
solution  are  drawn  out  with  an  ordinary  dropper,  and 
floated  upon  a  few  drops  of  pure  nitric  acid  in  a  nar- 
row test-tube. 

Note  the  time  when  the  nitric  acid  ceases  to  give  a 
coagulum  of  albumen,  or  when  the  albumen  disappears. 
We  thus  get  for  the  calculation  the  weight  of  the  egg- 
albumen,  A  ;  the  weight  of  the  pepsin  taken,  P\  and 
the  time  consumed,  T.  We  next  assume  the  standard 
time  of  3  hours,  the  average  time  of  stomach  digestion. 
The  relation  between  the  quantities  of  albumen  and 

A 

pepsin  is  expressed  by  the  fraction  — ;  that  is,  it  is 


28O       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

found  by  dividing  the  amount  of  albumen  by  the 
weight  of  the  pepsin. 

This  result  gives  the  amount  of  albumen  digested  by 
one  part  of  pepsin,  in  the  time  observed  in  the  experi- 
ment. 

To  calculate  what  this  would  digest  in  the  standard 
time,  we  must  multiply  the  above  ratio  by  the  ratio  of 
the  observed  time  to  the  standard  time ;  or,  to  put 
this  in  the  form  of  an  equation,  we  have  D  (or  digest- 

A        I* 
ive  power)  —  ~  x  y. 

Suppose  50  cc.  of  solution  (a)  containing  5  gms.  of 
egg-white  be  taken,  and  that  i  cc.  of  solution  (b)  be 
taken  containing  0.02  gms.  of  pepsin  and  that  the  time 
required  for  the  digestion  is  2  hours. 

If  we  substitute  these  quantities  in  the  above  equa- 
tion, we  have  £>  =  —  X  -  =  —  =  37$  gms.  That  is, 

.02          2         .04 

I  gm.  of  this  pepsin  is  capable  of  digesting  375  gms.  of 
egg-albumen  in  3  hours,  or  750  gms.  in  6  hours. 

As  egg-white  contains  about  12.2  per  cent,  of  dry 
albumen,  I  gm.  of  this  pepsin  will  digest  45-7  gms.  of 
dry  albumen  in  3  hours. 

This  method  gives  an  exact  statement  of  results,  re- 
quires little  if  any  skill  in  manipulation,  requires  no 
shaking,  and  the  results  are  uniform. 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       28 1 


CHAPTER  XXVII. 

DETERMINATION    OF   THE    DIASTASIC   VALUE    OF 
MALT  EXTRACTS  AND  PANCREATIC  EXTRACTS. 

A  ONE-PER-CENT.  solution  of  starch-mucilage  is  em- 
ployed. This  is  prepared  by  boiling  lo  gms.  of  pure 
starch  in  water,  cooling  and  making  up  to  1000  cc. 

10  cc.  of  this  standard  mucilage  is  mixed  in  a 
beaker  with  90  cc.  of  water.  The  mixture  is  then 
warmed  to  about  40°  C.  (104°  F.),  and  a  measured 
amount  of  the  malt  extract  or  pancreatic  extract  is 
added,  the  exact  time  of  adding  it  being  noted.  At 
short  intervals,  say  every  half-minute,  a  drop  of  the 
mixture  is  placed  upon  a  plate  or  white  slab,  with  a 
drop  of  a  dilute  aqueous  solution  of  iodine.  As  long 
as  starch  is  present  in  the  solution  a  blue  color  will  be 
produced  when  brought  in  contact  with  a  drop  of 
iodine  solution. 

When  all  the  starch  is  converted  by  the  pancreatic 
extract  into  erythro-dextrin,  the  blue  color  no  longer 
appears  and  a  pink  or  brown  color  is  produced  ;  when 
all  the  erythro-dextrin  disappears,  no  color  is  produced 
with  the  iodine.  This  is  termed  the  achromic  point. 
This  point  should  be  reached  at  the  end  of  not  less 
than  six  minutes,  in  order  that  the  end  reaction  may 
be  determined  with  sharpness.  When  it  takes  longer, 
the  change  is  too  gradual  to  be  exactly  determined. 


282       A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

In  the  statement  of  results  we  employ  the  following 
formula  : 

1>=-X  i 

~px  r 

In  this, 

5  =  the  weight  of  the  starch  employed  ; 
P  =  the  weight  of  pancreatic  extract  or  malt  extract 

employed  ; 
T  =  the  observed  time  from  the  addition  of  the  pan- 

creatic or  malt  extract  to  the  a  chromic  point  \ 
5  =  the  arbitrarily  chosen  standard  of  time  in  minutes. 
Example.  —  10  cc.  of  starch-mucilage  were  taken  and 
o.i  gm.  of  pancreatic  extract  was  added,  and  the  time 
required  to  reach  the  achromic  point  was  three  minutes. 
The  above  formula  would  become 


of  the  starch-mucilage  digested  by  I  gm.  of  the  extract 
in  five  minutes. 

As  10  cc.  of  the  solution  of  starch  contains  o.i  gm. 
of  dry  starch,  166.66  cc.  contain  1.666  gm.  This 
method  is  equally  applicable  to  malt  diastase,  salivary 
diastase,  or  pancreatic  diastase.  As  malt  extract  is 
not  official,  no  standard  of  strength  has  been  fixed. 
A  good  dry  extract  of  malt,  however,  should  digest 
its  own  weight  of  starch  in  twelve  minutes. 

Attfield  says  that  1.5  gm.  malt  should  digest  I  gm. 
of  starch  within  £  hour,  with  the  usual  quantity  of 
water,  at  60°  C. 

The  following  standard  of  a  recent  German  authority 
is  to  be  preferred.  To  0.6  gm.  of  starch  gelatinized 
with  60  cc.  of  water  and  heated  to  40°  C.  there  is 


A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       283 

added  0.5  gm.  of  the  extract,  dissolved  in  about  12  cc. 
of  water.  No  color  should  be  produced  by  iodine  in 
a  drop  of  the  solution,  at  the  end  of  fifteen  minutes. 
If  we  substitute  these  numbers  in  the  above  formula, 
we  have 

0.6        5        3.0 

-  X  —  =  --  =  0.4  gm.; 
0-5       15       7-5 

or  i  gm.  of  a  fairly  good  extract  by  this  test  should 
digest  0.4  gm.  of  starch  in  five  minutes.  This  is 
equivalent  to  the  statement  that  I  gm.  should  digest 
I  gm.  of  starch  in  twelve  minutes. 

The  method  used  in  the  laboratory  of  Parke  Davis 
&  Co.  is  as  follows  : 

Fill  six  or  more  two-ounce  vials  with  two  ounces  of 
distilled  water  and  two  drops  of  iodine  solution.  The 
iodine  solution  is  prepared  from  2  gm.  of  iodine,  4  gm. 
potassium  iodide,  250  gm.  of  water. 

5  gm.  of  corn-starch  are  now  mixed  with  30  gm. 
of  water,  and  after  thoroughly  stirring  the  mixture,  in 
order  to  have  all  the  starch  in  suspension,  it  is  poured 
into  150  cc.  boiling  water  and  the  mixture  brought  to 
the  boiling-point,  and  the  boiling  continued  for  a  min- 
ute, until  all  the  starch-granules  have  burst,  forming  a 
uniform  mucilaginous  solution ;  it  is  then  cooled  to 
100°  F. 

5  gm.  of  malt  extract  are  dissolved  in  50  cc.  of 
water.  \2\  cc.  of  this  solution,  representing  i¥  gm.  of 
malt  extract,  are  added  to  the  starch  solution,  which 
is  placed  on  a  water-bath,  and  maintained  at  a  tem- 
perature of  100°  F.  during  the  test.  At  the  expiration 
of  the  first  five  minutes  two  drops  of  the  mixture  are 
transferred  by  means  of  a  nipple  pipette  to  one  of  the 


284      A  TEXT-BOOK   OF    VOLUMETRIC   ANALYSIS. 

two-ounce  vials  containing  the  iodine.  The  bottle  is 
shaken  and  the  result  noted.  This  is  repeated  at  in- 
tervals of  one  minute,  until  two  drops  of  the  solution 
no  longer  produce  a  blue  coloration  with  the  dilute 
iodine  solution,  nor  more  than  a  faint  purple  from  the 
formation  of  intermediate  products  following  the  con- 
version of  the  starch. 

The  requirement  is  that  the  malt  shall  convert, 
according  to  this  test,  four  times  its  weight  of  starch  in 
ten  minutes. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       285 


CHAPTER  XXVIII. 
ESTIMATION   OF   ALKALOIDS   (VOLUMETRICALLY). 

IN  making  alkaloidal  assays  of  drugs  it  has  long 
been  the  custom  to  evaporate  the  final  ethereal  or 
chloroformic  extract,  and  to  weigh  the  residue  as  alka- 
loid. This  residue  seldom  if  ever  consists  of  the  pure 
alkaloid,  and  the  amount  of  impurity  is  very  variable  ; 
consequently  gravimetric  results  were  in  many  cases 
very  wide  of  the  truth,  and  hence  unreliable. 

The  volumetric  methods  are  in  most  cases  much 
more  satisfactory. 

While  the  results  of  the  titration  of  the  total  alka- 
loids of  drugs  cannot  be  called  absolutely  accurate, 
nevertheless  experience  has  shown  that  they  are  nearer 
the  truth  than  those  obtained  by  the  gravimetric 
method. 

In  estimating  an  alkaloid  by  titration,  it  is  essential 
to  know  the  formula  and  molecular  weight  of  the  alka- 
loid, as  well  as  the  equivalent  of  acid  with  which  it 
will  combine. 

In  the  case  of  drugs  where  two  or  more  alkaloids 
are  present,  accurate  results  can  only  be  obtained  by 
determining  how  much  of  each  alkaloid  is  present  by 
a  separate  assay.  But  as  a  rule  it  is  assumed  that  the 
alkaloids  are  present  in  equal  quantities,  and  the  mean 
of  their  molecular  weights  is  taken  as  the  basis  for  the 
calculation. 


286       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

If  the  alkaloid  be  from  a  recent  extraction,  and  is  in 
the  form  of  a  free  alkaloid,  it  is  dissolved  in  a  measured 

N 

quantity  of  -  -  hydrochloric-acid  solution,  and  the  ex- 
cess of  acid  solution  then  determined  by  residual  titra- 

N 
tion  with  —  sodium   hydroxide  solution,  using  as    an 

indicator  a  decoction  of  Brazil  wood  or  some  other 
suitable  reagent. 

Then  by  deducting  the  quantity  of  the  alkali  solu- 
tion used,  from  the  quantity  of  acid  solution  first 
added,  the  quantity  of  the  latter  which  combined  with 
the  alkaloid  is  obtained,  and  from  this  the  quantity  of 
alkaloid  present  may  be  calculated. 

A  molecular  weight  of  a  monobasic  acid,  or  half  of 
a  molecular  weight  of  a  dibasic  acid,  will  combine  with 
and  neutralize  a  molecular  weight  of  an  alkaloid,  pro- 
vided the  alkaloid  is  a  monacid  base. 

If  the  alkaloid  is  a  diacid  base,  one  molecular  weight 
will  combine  with  two  molecules  of  a  monobasic  acid 
or  one  molecular  weight  of  a  dibasic  acid. 

Sparteine  and  Emetine  are  diacid  alkaloids;  most 
of  the  others  are  monacid  bases. 

N 
Thus   1000  cc.  of  —  hydrochloric  acid  will  combine 

with  -g-1^  of  the  molecular  weight  of  a  monacid  alkaloid, 
or  ^L  of  the  molecular  weight  of  a  diacid  alkaloid,  as 
the  following  equations  show  : 

(Quinine.) 

CMH,,NA  +  HC1  =  C,HBN,0,HCL 

20)324  gms.          20)36.4  gms.  or  1000  cc.  —  acid. 
i6.2gms.  N 

1.82  gms.  or  looo  cc.  i — acid. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       287 
(Sparteine.) 

CBHQ6N,  +  2HC1  =  C5H26N2(HC1), 
2)114  2)72.8 

20)  57 


2.85  gms.     1.82  gms.  or  1000  cc.  —  acid. 

A.  H.  Allen  states  :  "  In  titrating  an  alkaloid  with 
methyl-orange  as  indicator  it  is  rarely  convenient  to 
employ  an  aqueous  solution  of  the  base. 

"A  solution  in  proof-spirit  can  be  employed,  but  the 
indicator  is  much  less  sensitive  under  sucli  conditions. 

"I  have  found  it  preferable,  especially  when  an  alka- 
loid is  much  colored,  as  is  frequently  the  case  in  assay- 
ing bases  directly  extracted  from  their  sources,  to  dis- 
solve the  alkaloid  in  a  little  chloroform,  ether,  amylic 
alcohol,  or  other  suitable  immiscible  solvent. 

"  The  solution  is  placed  in  a  small  stoppered  cylinder, 
together  with  a  few  cc.  of  water  colored  with  a  drop  or 
two  of  methyl-orange.  Then  on  gradually  running  in 
the  standard  acid  from  a  burette,  and  agitating  thor- 
oughly after  each  addition,  it  is  easy  to  observe  the 
end  of  the  reaction,  as  the  coloring  matter  remains  in 
the  immiscible  layer,  and  presents  a  marked  contrast 
to  the  red  color  of  the  aqueous  liquid." 

Allen  has  obtained  satisfactory  results  with  aconitine 
and  its  allies,  even  when  working  on  as  little  as  0.030 

N 
gm.,  by  using  ether  as  a  solvent,  and  titrating  with  — 

hydrochloric  acid. 

Prof.  P.  C.  Plugge  estimates  the  alkaloid  by  titrat- 
ing the  acid  of  the  salt  of  the  alkaloid  with  standard 
alkali,  and  from  the  result  calculates  the  quantity  of 
alkaloid  present.  He  first  determines  the  uncombined 
(free)  acid  by  titrating  with  standard  alkali  in  the  pres- 
ence of  litmus. 


288       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

He  then  titrates  another  portion  of  the  solution  in 
the  presence  of  phenolphthalein  to  determine  the 
total  quantity  of  acid  (both  free  and  combined)  pres- 
ent, and  from  this,  indirectly,  the  quantity  of  alkaloid 
is  calculated. 

For  the  estimation  of  the  alkaloid  in  a  commercial 
salt,  such  as  quinine  sulphate,  strychnine  sulphate,  etc.: 

Dissolve  the  salt  in   hot  water,  and  titrate  with 

20 

sodium-hydroxide  solution,  using  phenolphthalein, 
methyl-orange,  or  some  other  suitable  indicator. 

The  acid  in  combination  with  the  alkaloid  acts  as 
though  it  were  a  free  acid,  and  may  be  readily  esti- 
mated by  this  method. 

Methyl-orange  is  the  best  indicator  for  alkaloids,  as 
it  shows  an  alkaline  reaction  with  most  of  them. 

Phenolphthalein  should  be  used  with  caution,  as  an 
indicator,  in  titrating  morphine,  as  this  alkaloid  has  a 
faint  acid  reaction  with  it. 

It  is  sometimes  preferable  to  titrate  the  solution  of 

N 

alkaloidal   salt   with  -       NaOH     in    the    presence    of 
20 

phenolphthalein  to  exact  neutrality.  The  alkaloid  is 
now  in  a  free  state  in  a  neutral  liquid,  and  may  be 

N 

titrated  with  —  HC1  in  the  presence  of  methyl- 
orange. 

Prof.  Plugge  made  a  number  of  experiments  with  a 
view  to  determine  the  possibility  of  estimating  volu- 
metrically,  the  amount  of  acid  contained  in  alkaloidal 
salts,  and  from  this  determining  the  amount  of  alkaloid. 
He  finds— 

(i)  That  in  the  salts  of  the  weak  opium  bases  narco- 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       289 


tine,  papaverine,  and  narceine  the  amount  of  acid  can 
be  volumetrically  estimated  with  either  litmus  or  phe- 
nolphthalein,  the  reaction  being  as  precise  and  well  de- 
fined as  if  no  alkaloid  were  present. 

(2)  That  in  the   salts  of   alkaloids   in   general,   the 
acid  can  be  readily  determined  by  the  use  of  phenol- 
phthalein,  the  volatile  alkaloids  coniine  and    nicotine 
being  exceptions ;  and  that  in  the  case  of   morphine, 
brucine,  codeine,  and  thebaine,  phenolphthalein  may  be 
used  with  certain  restrictions. 

(3)  That    the  free   acid    in    solutions    of   alkaloidal 
salts  can  be  determined  by  the  use  of  litmus,  but  in 
solutions  of  weak  opium  bases   litmus  cannot  be  used. 
The  entire  quantity  of   acid,  both  free   and  combined, 
may  be  determined  by  the  use  of  phenolphthalein.    The 
difference  between  the  two  titrations  gives  the  quantity 
of  acid  united  to  the  base. 

TABLE  SHOWING  BEHAVIOR  OF  SOME  OF  THE  ALKALOIDS 
WITH  INDICATORS. 


Name. 

Formula. 

Methyl- 
orange. 

Phenolphthalein 

Litmus. 

Aconitine  
Atropine.. 
Brucine       . 

C8sH46N012 
C17H23N03 
C23H28N204 

C17H21N04 

C18H31N03 
C8H16N 
C17H19N03 
C5H7N 
C20H24N20, 
C21H22N2Oa 

Alk 

aline 

Neutral 

Alkaline 

Neutral 
« 

Alkaline 

Faintly  acid 
Alkaline 

Neutral 
« 

Alk; 

iline 

Cinchona  bases.. 
Cocaine  

Codeine  

Coniine        . 

Morphine         .  . 

Nicotine    

Quinine   

Strychnine 

Urea  is  neutral  to  methyl-orange,  phenolphthalein,  and  litmus. 
Caffeine  is  neutral  to  phenolphthalein  and  litmus.  Antipyrine  is  neu- 
tral to  phenolphthalein  and  litmus.  Pyridine  is  neutral  to  phenolph- 
thalein and  alkaline  to  litmus. 


290       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


TABLE  SHOWING  THE  FACTOR    FOR  VARIOUS  ALKALOIDS  WHEN 

TITRATING  WITH  —  ACID  OR  ALKALI. 
20 


Name. 

Formula. 

Molecular 
Weight.* 

Factor. 

C33H45NOu 

6j.7 

O  O^21C 

Atropine        <  •    • 

r,,Ho,NO« 

280 

U«UJ^^D 

Brucine       .    ... 

C,,H,«NoOA 

Cinchonine      

CioHaaNaO 

JV4 
2OJ. 

Cinchonidine  

daHaaNaO 

*y4 

2OJ. 

OOI.17 

Ci7H3,NO4 

^y4 
qo^ 

o  015  15 

Codeine               .  .  .  . 

CiaHo.NOo 

2QQ 

C8H1BN 

*y» 

joe 

Emetine    

j  C30H44N3O4  (Glenard) 

496 

0.0124 

(  C3oH4oN2O5  (Kunz) 

Ci7H3iNO4 

508 
1O1 

0.0127 

o  01515 

Hyoscyamine  

C,6H33NO3 

261; 

O  OI  "325 

Morphine  

Ci7H19NO3 

>8« 

o  01425 

Nicotine  

C6H,N 

81 

o  00405 

Pilocarpine  

C,iHi«,N2Oa 

208 

o  0104 

Quinine         . 

C20H34N3Oa 

•aoj. 

o  0162 

Sparteine  ....        . 

Ci6H3«N2 

lid. 

o  00285 

Strychnine      

CaiH32NaOa 

•5-74 

o  0167 

ESTIMATION     OF  ALKALOIDS     BY   MAYER'S    REAGENT. 

The  results  of  titrating  with  Mayer's  solution  have 
only  an  approximate  value,  being  influenced  to  a  large 
extent  by  various  conditions,  such  as  degree  of  dilution, 
mode  of  conducting  the  ojferation,  and  the  length  of 
time  allowed  for  precipitation  after  each  addition  of 
the  reagent. 

The  Mayer's  solution  is  added  from  a  burette,  and 
the  precipitate  allowed  to  subside  after  each  addition 
until  no  further  precipitation  takes  place,  which  can 
be  seen  by  bringing  a  drop  of  the  clear  supernatant 
liquid  in  contact  on  a  watch-glass,  with  two  or  three 
drops  of  the  reagent. 

A  more  common  practice  is  to  filter  the  solution 
after  each  addition  of  the  reagent,  using  the  same  filter. 


A  TEXT  BOOK   OF  VOLUMETRIC   ANALYSIS.       2QI 

When  10  cc.  of  the  filtered  liquid  are  no  longer  affected 
by  two  drops  of  the  reagent,  the  titration  is  complete. 

If  a  considerable  length,  of  time  is  allowed  to  elapse 
after  each  addition  of  reagent,  it  is  found  that  the  re- 
sults of  a  titration  will  coincide  more  nearly  with  what 
theory  requires;  but  the  principal  advantage  which  vol- 
umetric analysis  has  over  gravimetric,  namely,  rapidity 
of  execution,  is  thereby  forfeited. 

The  presence  of  alcohol,  free  acetic  acid,  or  ammonia 
vitiates  the  result ;  but  gum,  albumen,  glucose,  or  extrac- 
tives in  moderate  quantities  have  no  effect  upon  the 
reaction. 

In  all  comparative  titrations  with  this  reagent  the 
dilution  of  the  alkaloidal  solution  should  be  the  same. 
The  solution  should  be  slightly  acid,  and  its  strength 
about  1-200. 

In  titrations  where  the  end  reaction  can  only  be 
ascertained  by  the  cessation  of  the  formation  of  a  pre- 
cipitate, it  is  often  necessary  to  filter  a  por- 
tion of  the  turbid  solution  at  intervals  dur- 
ing the  titration,  and  test  it  to  see  whether 
the  process  is  completed.  In  such  cases 
Beale's  filter,  Fig.  29,  may  be  used.  Over 
the  lower  end  of  this  instrument  a  piece  of 
filter-paper  is  tied,  and  over  that  a  piece  of 
thin  muslin  to  keep  the  paper  from  being 
broken.  When  dipped  into  a  turbid  mixture 
the  clear  liquid  rises,  and  may  be  poured  out 
of  the  little  spout  for  testing.  If  the  proces8 
is  shown  to  be  unfinished,  the  contents  are  washed 
back  to  the  bulk  of  the  liquid,  and  small  portions 
filtered  out  at  intervals  until  the  process  is  found  to  be 
completed. 


2Q2       A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

The  Decinormal  Mayer's  Solution  is  made  as  fol- 
lows : 

N 

—  Mercuric  Potassium  Iodide  V.  S.,  U.  S.  P.— Hgla-f 

2KI  =  783.98.     39.2  gms.  in  a  litre. 

Dissolve  13.546  gms.  of  pure  mercuric  chloride  in 
600  cc.  of  water,  and  49.8  gms.  of  potassium  iodide  in 
100  cc.  of  water. 

Mix  the  two  solutions,  and  then  add  enough  water 
to  make  the  mixture  measure  at  or  near  15°  C.  (59°  F.) 
exactly  1000  cc. 

The  reaction  which  takes  place  when  these  two  solu- 
tions are  mixed  is 

HgCl,  +  4KI  ==  Hgl,  +  2KI  +  KC1. 

A.  B.  Lyons  and  many  others  prefer  to  use  a  solution 
of  half  the  above  strength. 

Each  cc.  of  the  decinormal  solution,  according  to 
Dr.  Mayer,  precipitates  of — 


gnr 

Aconitine. . .  0.0267 
Atropine.. . .  0.0145 
Brucine  ....  0.0233 
Cinchonine  .  0.0102 


gm. 

Coniine.  .  .  0.00416 
Morphine..  0.0200 
Narcotine..  0.0213 
Nicotine. . .  0.00405 


gm. 

Quinidine. . .  0.0120 
Quinine  . . .  0.0108 
Strychnine. .  0.0167 
Veratrine.  . .  0.0269 


The  precipitates  are  hydriodates  of  the  alkaloids,  re- 
spectively, with  iodide  of  mercury;  but  Lyons  finds 
that  they  are  not  of  definite  composition,  though  the 
variation  is  very  slight.  This  reagent  will  give  similar 
precipitates  with  all  of  the  alkaloids,  except  perhaps 
colchicine,  caffeine,  and  digitaline. 

ALKALOIDAL  ASSAY   BY   IMMISCIBLE  SOLVENTS. 

Many  alkaloids  are  soluble  in  certain  liquids  in  which 
their  salts  are  insoluble,  while  in  other  liquids  the  case 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       293 

is  reversed.  When  such  liquids  are  not  miscible  the 
separation  may  be  effected  by  the  so-called  "  shaking- 
out  process." 

In  many  cases  the  extraction  or  separation  may  be 
effected  by  adding  to  the  concentrated  aqueous  extract, 
a  suitable  alkaline  precipitant,  such  as  ammonia  water 
or  sodium-carbonate  solution,  which  liberates  the  alka- 
loid, then  shaking  up  with  some  solvent,  such  as  chloro- 
form, ether,  benzine,  benzol,  or  amylic  alcohol.  The 
liberated  alkaloid  is  thus  dissolved  or  washed  out  of 
the  aqueous  solution. 

The  alkaloid  may  be  again  abstracted  from  this  solu- 
tion by  the  addition  of  a  dilute  acid,  which  forms  again 
a  salt  of  the  alkaloid. 

In  the  U.  S.  P.  chloroform  is  exclusively  used  as  a 
solvent  for  alkaloids. 

The  extraction  is  directed  to  be  performed  in  a  glass 
separator  or  separatory  funnel,  which  consists  of  an 
elongated  (globular,  cylindrical,  or  conical) 
glass  vessel,  provided  .with  a  well-fitting 
stopper  and  an  outlet-tube  containing  a 
well-ground  glass  stop-cock.  (See  Fig.  30.) 

When  the  alkaloidal  solution,  suitably 
prepared,  is  introduced  into  the  separator, 
and  the  chloroform  subsequently  added,  the 
latter,  owing  to  its  higher  specific  gravity, 
will  form  the  lower  layer. 

If  the  two  are  violently  shaken  together 
there  will  often  result  an  emulsion,  which 
will  separate  slowly,  and  often  imperfectly.      FIG.  30. 
This   is   particularly  liable  to  happen   if   the  aqueous 
liquid    containing   the  alkaloid,   either  in   solution   or 
suspension,  is  strongly  alkaline,  or  has  a  high  specific 


2Q4      A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

gravity.  To  avoid  this  formation  of  an  emulsion  it  is 
better  to  frequently  invert  the  separator  or  to  rotate 
it  rapidly  than  to  shake  it  violently. 

The  emulsion  may  sometimes  be  destroyed  by  the 
addition  of  more  of  the  solvent,  and,  if  necessary,  aided 
by  the  application  of  gentle  heat,  or  by  the  introduc- 
tion of  a  small  quantity  of  alcohol  or  hot  water. 

On  withdrawing  the  chloroform  solution  of  an  alka- 
loid from  the  separator,  a  small  amount  of  the  solution 
will  generally  be  retained  in  the  outlet-tube  by  capil- 
lary attraction.  If  this  were  lost  the  results  of  the 
assay  would  be  seriously  vitiated.  To  avoid  this  loss, 
several  successive  small  portions  of  chloroform  should 
be  poured  into  the  separator  without  agitation,  and 
drawn  off  through  the  stop-cock  to  wash  out  the  out- 
let-tube. 

Another  source  of  loss  is  due  to  the  pressure  gener- 
ated in  the  separator  by  the  rise  of  temperature  caused 
when  an  alkaline  and  an  acid  liquid  are  shaken  together. 
Some  of  the  liquid  adheres  to  the  juncture  of  the 
stopper  and  neck,  and  when  the  stopper  is  loosened 
some  of  the  liquid  is  ejected. 

When  an  alkaline  carbonate  is  used  instead  of  caus- 
tic alkali  for  liberating  the  alkaloid,  the  liquids  should 
be  cautiously  and  gradually  mixed  by  rotation,  and  the 
separator  left  unstoppered  until  gas  is  no  longer  given 
off. 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.       295 


CHAPTER  XXIX. 

ESTIMATION  OF  THE  ALKALOIDAL  STRENGTH  OF 
SCALE  SALTS. 

FOUR  gms.  of  the  scales  are  dissolved  in  30  cc.  of 
water  in  a  capsule  with  the  aid  of  gentle  heat.  The 
solution  is  cooled  and  transferred  to  a  glass  separator  ; 
an  aqueous  solution  of  0.5  gm.  of  tartaric  acid  is  then 
added,  followed  by  an  excess  of  solution  of  sodium 
hydroxide.  The  tartaric  acid  prevents  the  precipita- 
tion of  Fe2(OH)8 ,  and  the  NaOH  sets  free  the  alkaloid. 
The  alkaloid  is  then  extracted  by  shaking  up  the  mix- 
ture with  successive  portions  of  chloroform,  15  cc.  each 
time.  The  chloroformic  layers  are  separated  each 
time  and  mixed,  evaporated  in  a  tared  capsule  on  a 
water-bath,  and  the  residue  dried  100°  C.  (212°  F.), 
and  weighed.  Or  the  residue  may  be  titrated  by  add- 
ing sufficient  decinormal  sulphuric  or  hydrochloric 
acid  to  dissolve  the  salts  and  still  remain  in  excess, 
then  titrating  residually  with  decinormal  NaOH  or 
KOH  to  determine  the  excess  of  acid. 

GENERAL  METHOD  FOR  THE   ESTIMATION   OF  THE 
ALKALOIDAL  STRENGTH    OF   EXTRACTS. 

One  gm.  of  the  extract  is  dissolved  in  20  cc.  of  water, 
heating  gently  if  necessary.  20  cc.  of  a  solution  con- 
taining 6  gms.  of  sodium  carbonate  are  added,  followed 


296      A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

by  20  cc.  of  chloroform.  Agitate,  warm  gently,  and 
separate  the  chloroform.  Add  to  this  20  cc.  of  dilute 
sulphuric  acid  with  an  equal  bulk  of  water,  again  agi- 
tate, warm,  and  separate  the  acid  liquor  from  the 
chloroform.  To  this  acid  liquor  add  an  excess  of  am- 
monia, and  agitate  with  20  cc.  of  chloroform.  When 
the  liquors  have  separated,  transfer  the  chloroform  to 
a  weighed  dish,  and  evaporate  over  a  water-bath. 
Dry  the  residue  for  one  hour  at  100°  C.  (212°  F.),  and 
weigh.  This  process  may  be  extended  to  almost  any 
extract  containing  alkaloids,  except  opium.  If  the  resi- 
due consists  of  only  one  alkaloid,  the  formula  and 
molecular  weight  of  which  are  known,  it  may  be  titrated 
instead  of  weighed. 

Assay  of  Extract  of  Nux  Vomica. — Extract  of 
nux  vomica  dried  at  100°  C.,  2  gms. ;  alcohol ;  ammo- 
nia-water sp.  gr.  0.960,  water,  chloroform,  decinormal 
sulphuric  acid  V.  S.,  centinormal  potassium  hydroxide 
V.  S.,  of  each  q.  s. 

Put  2  gms.  of  the  dried  extract  of  nux  vomica  into 
a  glass  separator.  Add  to  it  20  cc.  of  a  previously 
prepared  mixture  of  2  volumes  of  alcohol,  I  volume  of 
ammonia-water,  and  I  volume  of  water.  Shake  the 
separator  until  the  extract  is  dissolved. 

Then  add  20  cc.  of  chloroform  and  agitate  during 
five  minutes.  The  chloroform  dissolves  the  alkaloids 
which  the  ammonia  liberated.  Allow  the  chloroformic 
solution  to  separate,  remove  it  as  far  as  possible,  pour 
a  few  cc.  more  of  chloroform  into  the  separator,  and 
without  shaking  draw  this  off  through  the  stop-cock  to 
wash  the  outlet-tube.  Repeat  the  extraction  with  two 
further  portions  of  chloroform  of  15  cc.  each,  washing 
the  outlet-tube  each  time  as  just  directed. 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       297 

Collect  all  the  chloroformic  solutions  in  a  wide 
beaker  ;  expose  the  latter  to  a  gentle  heat  on  a  water- 
bath  until  the  chloroform  and  ammonia  are  completely 
dissipated.  Add  to  the  residue  10  cc.  of  decinormal 
sulphuric  acid  measured  accurately  from  a  burette, 
stir  gently,  and  then  add  20  cc.  of  hot  water.  When 
solution  has  taken  place  add  2  cc.  of  Brazil-wood  T.  S. 
(The  sulphuric  acid  combines  with  the  alkaloids,  and 
forms  sulphates  of  the  alkaloids.) 

Now  carefully  run  into  this  solution  centinormal 
potassium  hydroxide  V.  S.  until  a  permanent  pinkish 
color  is  produced,  showing  a  slight  excess  of  the 
alkali.  Divide  the  number  of  cc.  of  centinormal  po- 
tassium hydroxide  used  by  10.  Subtract  the  number 

N 

found  from  10  (the  10  cc.  of  —  acid  first    used),  and 

10 

N 

the  number  of  cc.  of  the  —  acid  which  went  into  com- 

10 

bination  with  the  alkaloids  is  found. 

The  two  principal  alkaloids  of  nux  vomica  are 
strychnine  and  brucine,  and  it  is  assumed  that  they  are 
present  in  equal  proportions  ;  and  thus  the  factor  for 
total  alkaloids  is  found  by  taking  the  mean  of  their  re- 
spective molecular  weights: 

Strychnine,  334  2)7:28 

Brucine,         394  364 


364  gms.  of  the  total  alkaloids  of  nux  vomica  will 
neutralize  1000  cc.  of  normal  sulphuric  acid.  36.4  gms. 
will  neutralize  1000  cc.  of  decinormal  sulphuric  acid. 

Hence  each  cc.  of  decinormal  sulphuric  acid  used  in 
the  above  assay  represents  0.0364  gm.  of  an  equal 
mixture  of  strychnine  and  brucine.  And  by  multi- 


298       A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

plying  the  number  of  cc.  used  by  this  factor,  the 
quantity  of  these  alkaloids  in  the  2  gms.  of  extract 
taken  is  obtained,  and  this  quantity  multiplied  by  50 
will  give  the  percentage. 

The  extract  should  contain  15  per  cent  of  total  alka- 
loids by  the  above  assay. 

Fluid  Extract  of  Nux  Vomica  is  evaporated  to  a 
solid  extract,  and  then  assayed  by  the  above  pro- 
cess. 

Tincture  of  Nux  Vomica  is  assayed  by  evaporating 
IOO  cc.  to  dryness,  and  the  residue  then  tested  by  the 
above  process.  It  should  contain  0.3  gm.  of  alkaloids. 

Assay  of  Extract  of  Opium. — Extract  of  opium 
dried  at  100°  C.,4  gms. ;  ammonia-water,  2.2  cc. ;  alco- 
hol, ether,  water,  of  each  a  sufficient  quantity. 

Dissolve  the  extract  of  opium  in  30  cc.  of  water, 
filter  the  solution  through  a  small  filter,  and  wash  the 
filter  and  residue  with  water  until  all  soluble  matters 
are  extracted,  collecting  the  washings  separately. 
Evaporate  in  a  tared  porcelain  capsule  first  the  wash- 
ings to  a  small  volume,  then  add  the  first  filtrate,  and 
evaporate  the  whole  to  a  weight  of  10  gms.  Rotate 
the  concentrated  solution  about  in  the  capsule  until 
the  rings  of  extract  are  redissolved.  Pour  the  liquid 
into  a  tared  flask,  and  rinse  the  capsule  with  a  few 
drops  of  water  at  a  time  until  the  entire  solution 
weighs  15  gms. 

Then  add  8.5  cc.  of  alcohol,  shake  well,  add  20  cc.  of 
ether,  and  shake  again. 

Now  add  the  ammonia-water,  stopper  the  flask  with 
a  sound  cork,  shake  it  thoroughly  during  ten  minutes, 
and  set  it  aside  in  a  moderately  cool  place  for  at  least 
six  hours,  or  overnight. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

At  the  expiration  of  this  time  remove  the  stopper 
carefully,  and  brush  into  the  flask  any  crystals  which 
may  adhere  to  the  cork.  Place  two  rapidly  acting, 
plainly  folded  filters,  one  within  the  other,  in  a  small 
funnel,  wet  them  well  with  ether,  and  decant  upon  the 
inner  one,  the  ethereal  solution,  as  completely  as  pos- 
sible. 

Add  10  cc.  of  ether  to  the  contents  of  the  flask, 
rotate,  and  again  decant  upon  the  filter;  repeat  this 
operation  with  another  10  cc.  of  ether.  Then  pour  the 
liquid  in  the  bottle  upon  the  filter  in  small  portions  at 
a  time,  in  such  a  way  as  to  transfer  the  greater  portion 
of  the  crystals  to  the  filter.  When  the  liquid  has  passed 
through  transfer  the  remaining  crystals  to  the  filter  by 
rinsing  the  flask  with  several  small  portions  of  water, 
using  not  more  than  10  cc.  in  all. 

Apply  water  to  the  crystals  drop  by  drop,  until  they 
are  practically  free  from  mother-liquor,  and  afterwards 
wash  them  with  a  saturated  alcoholic  solution  of  mor- 
phine, added  drop  by  drop.  When  this  has  all  passed 
through  displace  the  remaining  alcohol  by  ether,  using 
about  10  cc.  or  more  if  necessary. 

Dry  to  a  constant  weight  at  a  temperature  not  ex- 
ceeding 60°  C.,  and  carefully  transfer  the  crystals  to  a 
tared  watch-glass  and  weigh  them.  The  weight  multi- 
plied by  25  gives  the  percentage  of  crystallized  mor- 
phine present  in  the  extract. 

Instead  of  drying  and  transferring  the  crystals  to  a 
watch-glass  as  above  directed,  the  filter  containing 
them  may  be  immersed  in  some  boiling  water  in  a 
beaker,  and  an  excess  of  decinormal  sulphuric  acid 
added  to  dissolve  the  crystals  (the  quantity  being 
noted) ;  a  few  drops  of  methyl-orange  are  then  added, 


3OO      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

and  the  mixture  titrated  with  decinormal  potassium 
hydroxide.  Deduct  the  quantity  of  the  latter  used 
from  the  quantity  of  decinormal  acid  first  added,  and 
the  quantity  of  decinormal  acid  which  combined  with 
the  morphine  is  found. 

1000  cc.  of  normal  acid  represents  one  molecular 
weight  of  the  alkaloid. 

1000  cc.  of  decinormal  acid  represents  one  tenth  of  a 
molecular  weight  of  the  alkaloid  (30.3  gms.) ;  thus  each 

N 
cc.  of  —   acid  represents  0.0303   gm.  of   crystallized 

morphine. 

The  number  of  cc.  used,  multiplied  by  this  factor 
gives  the  quantity  of  morphine  present  in  the  4  gms. 
of  extract  taken. 

This  multiplied  by  25  gives  the  per  cent,  of  crystal- 
lized morphine;  it  should  contain  18  per  cent. 

Assay  of  Tincture  of  Opium  (Laudanum). — Tinc- 
ture of  opium,  loo  cc.  ;  ammonia-water,  3.5  cc. ;  alco- 
hol, ether,  water,  each  a  sufficient  quantity.  Evaporate 
the  tincture  to  about  20  cc.,  add  40  cc.  of  water,  mix 
thoroughly,  and  set  the  liquid  aside  for  an  hour,  stirring 
occasionally  and  disintegrating  the  resinous  flakes  ad- 
hering to  the  capsule  ;  then  filter,  and  wash  the  filter 
and  residue  with  water,  collecting  the  washings  sepa- 
rately. Evaporate  first  the  washings  to  a  small  vol- 
ume, then  add  the  first  filtrate  and  evaporate  to  14 
gms.  Pour  the  liquid  into  a  tared  flask;  rinse  the  cap- 
sule, and  add  the  rinsings  until  the  entire  solution 
weighs  20  gms.  Then  add  12.2  cc.  of  alcohol;  shake 
well;  add  25  cc.  of  ether;  shake  again.  Now  add  the 
ammonia-water,  cork  well,  shake  for  ten  minutes,  and 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       301 

set  aside  for  at  least  six  hours  or  overnight,  so  that  the 
crystals  may  form. 

At  the  expiration  of  this  time  decant  the  ethereal 
layer  upon  a  double,  plain,  rapidly  acting  filter  pre- 
viously wet  with  ether;  add  10  cc.  of  ether  to  the  con- 
tents of  the  flask,  rotate,  and  again  decant.  Repeat 
this  operation  with  another  10  cc.  of  ether.  Then 
pour  the  liquid  in  the  bottle  upon  the  filter,  in  small 
portions  at  a  time,  so  as  to  transfer  the  greater  portion 
of  the  crystals  to  the  filter,  and  wash  the  remaining 
crystals  on  to  the  filter  with  the  aid  of  a  small  quantity 
of  water,  using  not  more  than  10  cc.  Then  wash  the 
crystals,  first  with  a  few  drops  of  water,  then  with  an 
alcoholic  solution  of  morphine,  and  finally  with  ether 
to  displace  the  alcohol.  Dry  the  crystals  to  a  con- 
stant weight  and  weigh  on  a  tared  watch-glass. 

If  100  gms.  of  tincture  have  been  operated  upon,  the 
weight  of  the  crystals  is  at  once  the  per-cent.  of  crys- 
tallized morphine.  The  yield  should  be  1.3  to  1.5  gms. 
of  morphine  from  100  cc.  of  tincture. 

Assay  of  Opium. — Opium,  in  any  condition  to  be 
valued,  10  gms.;  ammonia-water,  3.5  cc. ;  alcohol,  ether, 
water,  each  a  sufficient  quantity.  Introduce  the  opium 
(which,  if  fresh,  should  be  in  very  small  pieces,  and  if 
dry,  in  very  fine  powder)  into  a  bottle  having  a  ca- 
pacity of  300  cc. ;  add  100  cc.  of  water ;  cork  well. 
Agitate  the  bottle  frequently  during  twelve  hours  ;  then 
pour  the  whole  as  evenly  as  possible  upon  a  wetted 
filter  having  a  diameter  of  12  cm.,  and  when  the  liquid 
has  drained  off  wash  the  residue  with  water  carefully 
dropped  upon  the  edges  of  the  filter  and  contents  until 
150  cc.  of  filtrate  are  obtained.  Then  carefully  trans- 
fer the  moist  opium  back  to  the  bottle  by  means  of  a 


302       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

spatula,  add  50  cc.  of  water,  agitate  thoroughly  and 
repeatedly  during  fifteen  minutes,  and  return  the  whole 
to  the  filter. 

When  the  liquid  has  drained  off,  wash  the  residue  as 
before  until  the  second  filtrate  measures  150  cc.,  and 
finally  collect  about  20  cc.  more  of  a  third  filtrate. 

Evaporate  in  a  tared  capsule,  first  the  second  filtrate 
to  a  small  volume,  then  add  the  first  filtrate,  rinsing 
the  vessel  with  the  third  filtrate,  and  continue  the 
evaporation  until  the  residue  weighs  14  gms.  From 
this  point  proceed  exactly  as  in  the  assay  of  tincture 
of  opium. 

The  weight  of  the  crystals  obtained,  when  multiplied 
by  10,  represents  the  percentage  of  crystallized  mor- 
phine present  in  the  sample  of  gum.  Opium  should 
contain  9$;  the  powdered  not  less  than  13$  nor  more 
than  15$. 

Assay  of  Cinchona,  U.  S.  P.— (a)  For  Total  Alka- 
loids.— Cinchona,  in  No.  80  (or  finer)  powder  and  com- 
pletely dried  at  100°  C,  20  gms. ;  alcohol,  ammonia- 
water,  chloroform,  ether,  normal  sulphuric  acid  V.  S., 
potassium  hydroxide  V.  S.,  each  a  sufficient  quantity. 
20  gms.  of  the  cinchona  in  very  fine  powder  is  intro- 
duced into  a  bottle  provided  with  an  accurately  fitting 
glass  stopper,  and  to  this  is  added  200  cc.  of  a  pre- 
viously prepared  mixture  of  19  volumes  of  alcohol,  5 
volumes  of  chloroform,  and  i  volume  of  ammonia- 
water;  the  bottle  is  stoppered,  and  thoroughly  and 
frequently  shaken  during  four  hours.  The  liquid  is  then 
passed  through  a  plug  of  cotton  in  a  funnel  into 
another  bottle,  being  careful  that  there  occurs  no  loss 
by  evaporation. 

IOO  cc.  of  the  clear  filtrate  (representing   10  gms.  of 


A  TEXT-BOOK  OF   VOLUMETRIC   ANALYSIS.       303 

cinchona)  are  transferred  to  a  beaker  and  evaporated 
to  dryness.  The  crude  alkaloids  thus  obtained  are 
dissolved  in  10  cc.  of  water  and  4  cc.  of  normal  sul- 
phuric acid  with  the  aid  of  gentle  heat.  The  cooled 
solution  is  then  filtered  into  a  separator,  and  the 
beaker  and  filter  washed  with  water  until  the  washings 
no  longer  have  an  alkaline  reaction,  using  as  little 
water  as  possible. 

Now  add  5  cc.  of  potassium  hydroxide  V.  S.,  or  suf- 
ficient to  render  the  liquid  alkaline.  The  alkaloids  are 
thereby  reliberated,  and  may  be  shaken  out  by  chloro- 
form. 20  cc.  of  chloroform  are  first  added,  and  the 
extraction  repeated,  using  10  cc.  at  a  time,  until  a  drop 
of  the  last  chloroform  extraction  leaves  no  residue 
when  evaporated  on  a  watch-glass. 

The  chloroformic  extracts  are  then  mixed,  evapo- 
rated in  a  tared  beaker,  the  residue  dried  at  100°  C. 
(212°  F.),  and  weighed. 

The  weight  multiplied  by  10  will  give  the  percentage 
of  total  alkaloids  in  the  specimen  tested. 

The  volumetric  method  cannot  very  well  be  em- 
ployed here,  as  the  alkaloids  exist  in  varying  propor- 
tions and  are  very  numerous,  thus  making  it  difficult 
to  find  a  factor  which  will  answer  for  all  cases. 

(b)  For  Quinine. — Transfer  50  cc.  of  the  clear  filtrate 
remaining  over  from  the  preceding  process  (and  repre- 
senting 5  gms.  of  cinchona)  to  a  beaker,  evaporate  it 
to  dryness,  and  proceed  as  directed  in  the  assay  for 
total  alkaloids,  using,  however,  only  half  the  amounts 
of  volumetric  acid  and  alkali  there  directed. 

Add  the  united  chloroformic  extracts  containing  the 
alkaloids  in  solution,  gradually  and  in  small  portions  at 
a  time,  to  about  5  gms.  of  powdered  glass  contained  in 


304      A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

a  porcelain  capsule  placed  over  a  water-bath,  so  that 
when  the  contents  of  the  capsule  are  dry  all  or  nearly 
all  of  the  dry  alkaloids  shall  be  in  intimate  admixture 
with  the  powdered  glass,  and  the  chloroform  com- 
pletely expelled.  Now  moisten  the  residue  with  ether, 
and  having  placed  a  funnel  containing  a  filter  (7  cm.  in 
diameter)  and  well  wetted  with  ether  over  a  small 
graduated  tube  (A),  transfer  to  the  filter  the  ether- 
moistened  residue  from  the  capsule.  Rinse  the  latter, 
several  times  if  necessary,  with  fresh  ether,  so  as  to 
transfer  the  whole  of  the  residue  to  the  filter ;  then 
percolate  with  ether,  drop  by  drop,  until  exactly  10  cc. 
of  percolate  are  obtained.  Then  collect  another  10 
cc.  by  similar  slow  percolation  with  ether  in  a  second 
graduated  tube  (B).  Transfer  the  contents  of  the 
tubes  to  two  small  tared  capsules,  properly  marked  (A 
and  B),  and  evaporate  to  a  constant  weight  at  100°  C. 
(212°  F.)  and  weigh  them.  (The  residue  in  (A)  will  con- 
tain practically  all  of  the  quinine,  together  with  a  por- 
tion of  the  alkaloid  less  soluble  in  ether ;  the  residue 
in  (B)  will  consist  almost  entirely  of  these  alkaloids.) 

From  the  amount  of  residue  obtained  in  (A)  deduct 
that  contained  in  (B).  This  will  give  approximately  the 
amount  of  quinine  present  in  the  5  gms.  of  sample. 
Multiply  this  by  20  a-nd  the  percentage  of  quinine 
containing  one  molecule  of  water  is  obtained. 

Cinchona  calisaya  should  contain  not  less  than  5 
per  cent,  of  total  alkaloids,  and  at  least  2.5  per  cent,  of 
quinine. 

Cinchona  succirubra  should  contain  not  less  than  5 
per  cent,  of  its  peculiar  alkaloids. 

Assay  of  Fluid  Extract  of  Ipecac. — 8  gms.  of  the 
fluid  extract  are  diluted  with  8  gms.  of  water  in  an 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       305 

ordinary  vial,  32  gms.  of  chloroform  and  48  gms.  of 
ether  are  added  and  shaken  up ;  4  gms.  of  ammonia 
water  are  now  introduced,  and  the  mixture  frequently 
agitated  during  half  an  hour. 

Fifty  gms.  of  the  chloroform-ether  solution  (repre- 
senting 5  gms.  of  the  fluid  extract)  are  separated, 
poured  into  a  tared  flask,  and  the  solvent  distilled  or 
evaporated  off;  the  varnish-like  residue  is  twice  treated 
with  5  to  10  cc.  of  ether,  and  evaporated  by  forcing  a 
current  of  air  into  the  flask  by  means  of  a  rubber  bulb  ; 
the  residue  is  then  dried  in  a  water-bath  and  weighed. 
For  the  titration,  the  residue  may  be  dissolved  in  a 
known  quantity  of  decinormal  hydrochloric  acid ;  the 
solution  may  be  assisted  by  a  gentle  heat,  or  the  addi- 
tion of  a  small  quantity  of  alcohol;  10  or  12  drops  of 
Brazil-wood  T.  S.  are  then  added_  and  the  excess  of 
acid  determined  by  means  of  decinormal  alkali,  the 
latter  being  added  until  the  liquid  becomes  cardinal  to 
purplish  red  in  color. 

The  quantity  of  decinormal  alkali  used  is  then  sub- 
tracted from  the  quantity  of  decinormal  acid  first 
added.  This  gives  the  quantity  of  the  decinormal  acid 
which  was  used  to  neutralize  the  alkaloids  present. 

Emetine,  according  to  Kunz,  is  diacid,  and  has  the 
formula  C30H40N2O5,  molecular  weight  508.  Therefore 
one  molecule  of  emetine  will  neutralize  two  molecules 
of  hydrochloric,  or,  half  a  molecular  weight,  254  in 
grammes,  will  neutralize  I  litre  of  normal  hydrochloric, 
acid,  while  25.4  gms.  will  neutralize  1000  of  decinormal 
acid. 

Thus  each  cc.  of  decinormal  acid  represents  0.0254 

N 
gm.  of  emetine.     If  —  acid  is  used,  each  cc.  represents 

0.0127  gm.  of  emetine. 


306      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

C,.H,0NA  +  2HC1  =  CMH.0N,06(HC1)11. 

Emetine  (Kunz). 

2)508  2)72.79 

10)254  gms.      10)36.37  gms.  or  1000  cc.  _  y   g 

i 

2)  25. 4  gms.      2)  3  637  gms.  or  1000  cc.  _V.  S. 

10 

12.7  gms.  1.818  gms.  or  1000  cc.  —  V.  S. 

20 

Thus  if  decinormal  acid  is  employed,  the  number  of 
cc.  which  were  neutralized  by  the  alkaloid  when  mul- 
tiplied by  .0254  gm.  gives  the  quantity  of  emetine 
present  in  5  gms.  of  the  fluid  extract ;  and  when  this 
is  multiplied  by  20  the  percentage  is  obtained. 

Assay  of  Ipecac  Root. — 10  gms.  of  the  finely 
powdered  and  dried  root  are  placed  in  a  bottle  having 
a  capacity  of  about  150  cc. ;  40  gms.  of  chloroform  and 
60  gms.  of  ether  are  added,  and  shaken  well  for  several 
minutes ;  10  gms.  of  ammonia-water  are  now  added  ; 
this  liberates  the  emetine,  which  immediately  dissolves 
in  the  chloroform  and  ether,  while  the  suspended 
powder  settles  to  the  bottom  of  the  bottle.  The 
bottle  is  frequently  shaken  during  one  hour,  and  5  gms. 
more  of  ammonia-water  added  ;  the  powder  then  agglu- 
tinates in  a  lump,  and  the  liquid  becomes  perfectly  clear. 
50  gms.  of  the  chloroform-ether  solution  are  now  taken 
(representing  5  gms.  of  the  root)  and  transferred  to  a 
tared  flask,  and  the  process  completed  as  described 
under  the  assay  of  the  fluid  extract. 

The  titration  is  in  this  case  a  little  more  difficult  be- 
cause of  the  presence  of  fat  from  the  root.  It  is  advis- 
able to  extract  the  fat  from  the  root  before  subjecting 
it  to  this  assay. 

Estimation  of  the  Strength  of  Resinous  Drugs. 
— Take  5  to  IO  gms.  of  the  drug  in  powder,  and 


A   TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       307 

place  it  in  a  strong  glass  flask  with  100  cc.  of  pure 
alcohol  (U.  S.  P.  and  free  from  resin).  Close  the  flask 
with  a  good  cork,  and  digest  it  in  a  warm  place  at  about 
49°  C.  (120°  F.)  for  12  hours,  shaking  from  time  to 
time.  Pour  or  filter  off  80  cc.  (representing  -f^  of  the 
total  drug  taken),  place  it  in  a  weighed  beaker,  and 
evaporate  to  25  cc.  on  the  top  of  the  water-bath.  Now 
add  50  cc.  of  distilled  water,  and  boil  gently  over  a  low 
gas  flame  till  all  the  alcohol  is  driven  off.  Let  it  cool 
and  perfectly  settle,  pour  off  the  supernatant  liquor, 
wash  the  deposited  resin  by  decantation  with  hot  dis- 
tilled water,  and  then  dry  the  beaker  and  its  contents 
in  the  air-bath  at  105°  C.  (220°  F.)  and  weigh,  deduct- 
ing the  tare  of  the  beaker.  Thus  treated,  jalap,  for 
example,  should  show  12  per  cent  of  resin,  of  which 
not  over  10  per  cent  should  be  soluble  in  ether.  Scam- 
mony  should  show  75  per  cent  resin,  which  is  entirely 
soluble  in  ether  and  in  solution  of  potassa.  From  the 
latter  it  is  not  reprecipitated  by  dilute  hydrochloric 
acid  in  excess.  For  other  resinous  drugs  no  official 
standard  has  yet  been  laid  down. 


308      A   TEXT-BOOK   OF  VOI  I !  METRIC   ANALYSIS. 


CHAPTER    XXX. 
GLUCOSIDES. 

GLUCOSIDES  are  proximate  vegetable  principles, 
which  when  boiled  with  a  dilute  acid,  or  subjected  to 
some  other  method  of  decomposition,  take  up  the  ele- 
ments of  water,  and  yield  glucose  and  some  other  sub- 
stance, this  other  substance  differing  in  each  case 
according  to  the  particular  glucoside  operated  upon. 

Upon  this  property  of  these  bodies  is  based  a  method 
for  their  estimation. 

This  method  depends  upon  converting  the  glucoside 
into  glucose,  and  then  estimating  the  glucose  by  Feh- 
ling's  solution  in  the  usual  way,  and  from  the  amount 
of  glucose  formed  calculating  the  quantity  of  the  gluco- 
side. 

The  conversion  of  glucosides  into  glucose  is  shown 
by  the  following  equations  : 

C,,H,A  +  H,0  =  C.H.(OH)CH,  +  C.H.A. 

Salicin,  286.  Saligenol.  Glucose,  180. 

Thus  it  is  seen  that  180  gms.  of  glucose  are  derived 
from  286  gms.  of  salicin. 

C,,H,A>  +  2H,o  =  CISH,A  +  2C.H,,o, 

Digitalin.  Digitaliretin.  Glucose. 

Ca,H6A,  +  5H,0  =  C,.HM0,  +  3C.H.A- 

Jalapin.  Jalapinol.  Glucose. 

Q.H.A  +  H,0  =  C,,H,A  +  C.H.,0.. 

Glycyrrhizin.  Glycyrrhetin.       Glucose. 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.      309 


CHAPTER  XXXI. 
MILK. 

MlLK  is  the  nutritive  secretion  of  glands  (the  mam- 
mary glands)  which  are  characteristic  of  the  mam- 
malia. 

This  secretion  takes  place  as  a  result  of  pregnancy 
and  delivery,  and  continues  for  a  variable  period,  con- 
stituting the  entire  food  of  the  young  animal  until  it 
is  able  to  live  upon  other  foods. 

The  milk  of  'different  animals  contains  qualitatively 
identical  or  analogous  ingredients  to  that  of  the  cow, 
namely,  fat  (which  is  held  in  suspension),  nitrogenous 
matters  such  as  casein  and  albumen,  milk  sugar,  in- 
organic salts,  and  water. 

The  average  composition  of  cow's  milk  is  as  follows  : 

Fat 3.65  per  cent. 

Proteids   4.40    "       " 

Lactose 4.25    "       " 

Inorganic  salts 0.75    "       " 

Total  solids 13.05    "       " 

Water 86.95    "       " 

100.00 

In  the  milk  of  different  animals,  however,  these  in- 
gredients are  in  different  proportions,  as  the  following 
table  shows : 


0*  TOT 

TJFITlESltT! 


310       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


Human. 

Goat. 

Mare. 

Ass. 

Fat         

per  cent. 
34O 

per  cent. 
c  2 

per  cent. 
I  j 

per  cent. 

Proteids   

2  AC 

1  8 

2  2 

o  7 

Lactose 

5?c 

1     O 

e   « 

Inorganic  salts        . 

O  "3S 

O  7 

O<j 

•  J 

Water    

88  os 

86  o 

QO   6 

QO  6 

IOO.OO 

100.0 

IOO.O 

IOO.O 

Total  solids  

I  i.qsc 

14.0 

91 

O  J. 

Milk  is  a  perfect  natural  emulsion.  The  casein 
appears  to  be  the  emulsifying  agent,  a  film  of  which 
envelops  each  globule  of  fat,  thus  preventing  cohesion. 

The  inorganic  salts  are  chiefly  the  phosphates  of 
sodium  and  calcium,  and  the  chlorides  of  sodium  and 
potassium,  but  magnesium  and  iron  are  also  generally 
present. 

The  proteids  consist  mainly  of  casein  with  some  al- 
bumen, the  proportion  being  about  as  6  to  i. 

Besides  the  above-mentioned  constituents  milk  also 
contains  a  very  small  quantity  of  peptone,  kreatin, 
leucin,  etc.  Also  gases,  such  as  CO2 ,  O,  and  N. 

Colostrum  is  the  milk  secreted  in  the  early  stages 
of  lactation  ;  it  is  rich  in  proteids,  often  containing  as 
much  as  20  per  cent,  and  contains  a  few  corpuscles  of 
a  peculiar  character,  which  look  like  epithelium-cells, 
called  colostrum  corpuscles. 

Reaction. — The  reaction  of  the  milk  of  herbivorous 
animals  is  generally  alkaline,  that  of  carnivora  is  gener- 
ally acid.  The  reaction  of  cow's  milk  is  generally 
neutral,  sometimes  slightly  acid,  rarely  alkaline. 

Specific  Gravity. — This  varies  in  normal  cow's  milk 
from  1.029  to  1.035.  It  should  not  be  below  1.029. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       311 


An  excess  of  fat  lowers  the  specific  gravity  and  the 
removal  of  fat  raises  it.  Thus  skimmed  milk  has  a 
higher  specific  gravity  than  normal  milk. 

These  facts  are  made  use  of  for  the  detection  of  the 
ordinary  adulterations. 

Determinations  of  the  specific  gravity  of  milk  should 
always  be  made  at  the  temperature  of  60°  F.,  and  may 
be  made  by  any  of  the  ordinary  methods.  See  table 
of  corrections  for  temperatures  other  than  60°  F.,  page 
312.  A  special  hydrometer  known  as  the  lactometer  is, 
however,  generally  used.  The  lactometer  is  graded 
from  o°  at  the  top  to  120°  at  the  bottom.  In  taking 
the  specific  gravity  with  this  instrument  the  tempera- 
ture of  the  milk  must  be  60°  F. 

For  every  2^°  of  temperature  above  the  60°  standard, 
one  degree  is  to  be  added  to  the  reading  of  the  lactom- 
eter ;  below  60°  F.  a  similar  subtraction  is  to  be  made. 

On  the  lactometer  scale  o°  —  i.ooo,  the  specific 
gravity  of  pure  water;  at  60°  F.  100  =  1.029,  the 
specific  gravity  of  the  poorest  possible  milk  at  the 
same  temperature. 

If  in  a  sample  of  milk  the  lactometer  stands  at  80° 
the  sample  contains  about  80  per  cent  of  standard  milk 
and  20  per  cent  of  water.  If  the  lactometer  stands  at 
90°,  the  sample  contains  about  10  per  cent  of  water. 


Lactometer 
Reading. 

Specific  Gravity. 

Lactometer 
Reading. 

Specific  Gravity. 

0 

.0000 

70 

I.O203 

IO 

.0029 

80 

1.0232 

20 

.0058 

90 

I.026I 

30 

.0087 

IOO 

1.0290 

40 

.0116 

no 

1.0319 

50 

.0145 

120 

1.0348 

60 

.0174 

312 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


111 


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A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.      313 

The  Adulterations  of  Milk.— The  adulterations 
usually  practised  are  the  abstraction  of  cream  (skim- 
ming) or  the  addition  of  water,  or  both.  Occasion- 
ally the  addition  of  some  foreign  substance,  as  sodium 
carbonate,  borax,  common  salt,  or  sugar,  is  met  with  ; 
or  preservatives,  as  boric  or  salicylic  acids. 

The  detection  of  adulterations  usually  depends  upon 
the  determination  of  the  specific  gravity,  the  fat,  total 
solids,  and  the  ash. 

These  ingredients  are,  however,  present  in  milk  in 
varying  proportions,  and  hence  certain  limits  of  allow- 
able variations  have  been  determined  upon  from  time 
to  time. 

The  standard  adopted  in  many  States  in  this  country 
is,  for  specific  gravity,  not  less  than  1.029,  for  total  sol- 
ids, not  less  than  12  per  cent.,  for  fat  3  per  cent.  The 
total  solids  may  vary  legally  from  12  to  13.13  per  cent., 
and  the  solids  not  fat, "from  8.5  to  9.5  per  cent. 

Estimation  of  Total  Solids  and  Water.— A 
small,  shallow  platinum  or  porcelain  dish  about  ij- 
inches  in  diameter  is  heated  to  redness,  allowed  to  cool, 
and  weighed.  About  5  cc.  of  milk  are  then  put  in, 
and  again  weighed.  The  difference  between  the  two 
weighings  gives  the  weight  of  the  milk  taken.  Now 
place  the  dish  on  a  water-bath  and  heat  until  the  milk 
ceases  to  lose  weight.  Then  cool  again  and  weigh. 
The  weight  of  the  dry  residue  minus  the  tare  of  the 
dish  equals  the  total  solids. 

Then  by  multiplying  this  by  100,  and  dividing  by 
the  weight  of  milk  taken,  the  percentage  of  total  solids 
is  found.  Thus, 

total  solids  X  IOO 


weight  of  milk 


=  per-cent.  of  total  solids. 


314      A  TEXT-BOOK  OF   VOLUMETRIC   ANALYSIS. 

This    deducted     from      100     gives    the    per-cent.    of 
water. 

Fat. — Where  great  accuracy  is  unnecessary  the  fat 
may  be  determined  by  treating  the  total  solid  residue 
with  successive  portions  of  warm  ether  until  the  fat  is 
completely  dissolved  out.  The  ethereal  solution  is 
then  evaporated  and  the  fat  which  remains  behind  is 
weighed,  or  the  residue  in  the  dish  may  be  again 
weighed.  The  loss  of  weight  then  represents  the  fat. 
The  results  so  obtained  are  0.3  to  0.5$  too  low. 

Adams  Method  is  the  officially  recognized  method 
for  the  accurate  estimation  of  fat  in  milk. 

This  consists  essentially  in  spreading  the  milk  over 
absorbent  paper,  drying,  and  extracting  the  fat.  The 
paper  used  for  this  purpose  must  previously  have  been 
thoroughly  exhausted  with  alcohol  and  ether,  and 
should  be  in  long  narrow  strips. 

The  procedure  is  as  follows:*  5  cc.  of  the  milk  are 
put  into  a  small  beaker  and  weighed.  A  strip  of  the 
absorbent  paper  which  has  been  rolled  into  a  coil  is 
thrust  into  the  beaker  containing  the  milk.  In  a  few 
minutes  nearly  the  whole  of  the  milk  will  be  absorbed  ; 
the  coil  is  then  withdrawn,  and  stood  dry  end  down 
upon  a  sheet  of  glass. 

It  is  important  to  take  up  the  whole  of  the  milk 
from  the  beaker,  as  the  paper  has  a  selective  action, 
removing  the  watery  constituents  by  preference  over 
the  fat.  The  beaker  is  again  weighed,  and  the  milk 
taken  found  by  difference.  The  paper  charged  with 
the  milk  is  now  dried  in  a  water-oven  and  placed  in 
a  Soxhlet  extraction  apparatus  (Fig.  28).  About 
75  cc.  of  ether  are  introduced  into  the  tared  flask  of 
the  apparatus,  and  heat  applied  by  means  of  a 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.      315 

water-bath  and  continued  until  exhaustion  is  com- 
plete. The  flask  is  then  detached,  the  ether  removed 
by  distillation,  and  the  fat  which  remains  is  weighed. 

The  paper  may  be  charged  with  the  milk  by  spread- 
ing the  latter  over  the  surface  of  the  paper  by  means 
of  a  pipette. 

The  Werner- Schmid  Method. —  This  is  a  satisfactory 
and  at  the  same  time  a  rapid  method  for  the  determin- 
ation of  fat,  and  is  especially  suitable  for  sour  milk. 

10  cc.  of  the  milk  are  put  into  a  long  tube  having  a 
capacity  of  about  50  cc.,  and  10  cc.  of  strong  hydrochloric 
acid  are  added ;  or  the  milk  may  be  weighed  in  a  small 
beaker  and  washed  into  the  tube  with  the  acid.  The 
liquids  are  mixed  and  boiled  for  i£  minutes,  or  until  the 
liquid  turns  dark  brown,  but  not  black.  The  tube  and 
contents  are  then  cooled,  and  30  cc.  of  ether  are  added, 
shaken,  and  allowed  to  stand  until  the  acid  liquid  and 
ether  have  separated.  The  cork  is  now  taken  out  and 
the  wash-bottle  arrangement  inserted  (see  Fig.  27).  The 
stopper  of  this  should  be  of  cork,  not  of  rubber,  since  the 
ether  has  a  solvent  action  upon  the  latter.  The  lower 
end  of  the  exit  tube  is  adjusted  so  as  to  rest  immediately 
above  the  junction  of  the  two  liquids.  The  ethereal 
solution  of  fat  is  then  blown  off,  and  received  in  a 
weighed  beaker.  Two  more  portions  of  10  cc.  each 
are  shaken  successively  with  the  acid  liquid,  blown  out, 
and  added  to  the  first.  The  ethereal  solution  is  then 
heated  on  a  water-bath,  and  the  residue  of  fat  weighed. 
The  results  agree  quite  closely  with  the  Adams 
method. 

Calculation  Method. — This  rests  upon  the  assumption 
that  every  per-cent.  of  solids  not  fat,  raises  the  specific 
gravity  by  a  definite  amount,  while  every  per-cent.  of 


3l6     A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

fat  lowers  it  by  a  definite  amount.  An  accurate  de- 
termination of  the  per-cent  of  total  solids  and  of  the 
specific  gravity  therefore  furnish  the  necessary  data 
for  calculating  the  amount  of  fat. 

Hehner  and  Richmond  have  devised  the  following 
formula: 

F=o.S$gT-  0.2  1  86(9.  ; 

in  which  F  =  fat,  T  =  total  solids,  and  G  =  the  last 
two  units  of  the  specific  gravity  and  any  decimal. 
Thus  if  the  specific  gravity  is  1029,  G-will  be  29;  if 
1029.5,  G  will  be  29.5. 

Example.  —  Let  us  assume  in  the  examination  of  a 
certain  milk  that  the  specific  gravity  was  1030,  and 
that  it  contained  12  per  cent,  of  total  solids.  We  then 
have 

Fat  —  0.859  X  12  —  0.2186  X  30  =  3.75$ 

When  the  per-cent.  of  fat  is  known,  the  formula  may 
be  transposed  so  as  to  calculate  the  total  solids,  as 
follows  : 


0.859 

Example.  —  A  sample  of  milk  is  found  to  contain  3.75 
per  cent,  of  fat,  and  its  specific  gravity  is  1030  ;  then 

Total  solids  =  37L±o_£86_x  jo  = 
0.859 

Ash.  —  The  ash  may  be  determined  by  igniting  at  a 
dull-red  heat  the  residue  left  after  the  fat  has  been 
extracted  from  the  total  solids.  The  organic  matter  is 
thus  all  burned  off,  and  the  residue  is  weighed  and  cal- 
culated as  ash.  The  ash  should  be  about  0.75  per  cent, 
never  below  0.67. 

To  Calculate  the  Per  cent,  of  Pure  Milk  and  of 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.      317 

Added  Water,  the  following  formula  maybe  adopted, 
which  is  based  upon  the  legal  standard  of  the  State  of 
New  York,  which  is  based  upon  the  poorest  possible 
natural  milk,  viz.,  3  per  cent,  of  fat,  12  per  cent,  of  total 
solids,  and  9  per  cent,  of  "  solids  not  fat." 

If,  however,  a  milk  has  3  per  cent,  of  fat  and  only  8.5 
per  cent,  of  "  solids  not  fat,"  it  need  not  be  considered 
as  definitely  proved  to  be  adulterated. 

The  quantity  of  added  water  should,  however,  always 
be  calculated  upon  the  average  standard  of  9  per  cent 
"  solids  not  fat,"  provided  the  milk  is  certainly  well 
below  the  limit  of  8.5  per  cent. 

The  "solids  not  fat"  are  used  as  a  basis  for  the  cal- 
culation because  they  are  a  fairly  constant  quantity, 
the  fat  being  variable.  The  calculation  is  made  thus  : 

"  Solids  not  fat"  X  100 

---  =  p.  c.  or  pure  milk  present  ; 

and  the  difference  between  this  result  and  100  will  of 
course  give  the  added  water. 

Example.  —  A  sample  of  milk  upon  analysis  was 
found  to  contain  8.1  per  cent  of  solids  not  fat  ;  then 

8.1  X  ioo       810.0 


9  9 

of  pure  standard  milk  and  10  per  cent  of  water. 

Total  Proteids.  —  Rittenhausen  s  Copper  Process.  — 
The  solutions  required  are:  (i)  Copper-sulphate  solu- 
tion, 34.64  gms.  in  500  cc.  ;  (2)  Sodium-hydroxide  solu- 
tion, 12  gms.  to  500  cc. 

10  gms.  of  the  milk  are  diluted  to  ioo  cc.  with  dis- 
tilled water  and  placed  in  a  beaker  ;  5  cc.  of  the  cop- 
per-sulphate solution  are  now  added  and  thoroughly 
mixed. 


318      A  TEXT-BOOK   OF  VOLUMETPIC   ANALYSIS. 

The  sodium-hydroxide  solution  is  now  added  drop 
by  drop,  stirring  constantly  until  the  precipitate  settles 
quickty,  and  the  liquid  is  neutral  or  feebly  acid.  It 
should  never  be  alkaline,  as  an  excess  of  alkali  pre- 
vents the  precipitation  of  some  of  the  proteids. 

The  precipitate  which  includes  the  fat  carries  down 
all  of  the  copper.  It  is  washed  by  decantation  and 
collected  upon  a  weighed  dry  filter,  the  contents  of 
the  filter  being  washed  until  the  total  filtrate  measures 
about  250  cc.  This  filtrate,  which  contains  no  copper, 
is  reserved  for  the  determination  of  the  sugar  by  Feh- 
ling's  Solution. 

The  precipitate  is  washed  once  by  strong  alcohol  to 
remove  adhering  water;  it  is  then  washed  several  times 
with  ether  to  remove  the  fat.  The  residue  on  the 
filter,  which  consists  of  the  proteids  and  copper  hy- 
droxide, is  dried  at  265°  F.  in  the  air-bath  and  weighed. 
It  is  then  transferred  to  a  porcelain  crucible  and  incin- 
erated, and  the  residue  weighed. 

The  weight  of  the  filter  and  contents  less  the  weight 
of  the  filter  and  residue  after  ignition,  gives  the  weight 
of  the  proteids. 

The  Milk-sugar  is  estimated  in  the  mixed  filtrate 
from  the  precipitated  proteids  by  the  use  of  Fehling's 
Solution  in  the  usual  way.  (See  Estimation  of  Sugar.) 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       319 


CHAPTER   XXXII. 
BUTTER. 

THE  composition  of  commercial  butter  usually  varies 
within  the  following  limits  : 

Fat 78-94$ 

Curd 1-3 

Water 5-14 

Salt 0-7 

(Leffmann  and  Beam.) 

Reichert's  Process  for  the  detection  of  foreign  fat 
in  butter  is  undoubtedly  the  best. 

This  process  is  based  upon  the  presence  in  butter- 
fat  of  tributyrin,  which  yields  when  appropriately 
treated  an  acid  (butyric  acid),  which  is  relatively  much 
more  volatile  than  the  other  acids  yielded  by  any  of 
the  fats  which  may  be  used  for  the  adulteration  of 
butter. 

The  process  is  as  follows  :  2.5  gms.  of  the  butter  are 
melted  and  filtered  into  a  flask  having  a  capacity  of 
about  150  cc.,  20  cc.  of  a  5-per-cent  alcoholic  solution 
of  potassium  hydrate  are  added,  and  the  mixture  heat- 
ed to  gentle  ebullition  on  a  water-bath  until  the  fat  is 
entirely  saponified  and  the  alcohol  expelled. 

The  soap,  which  should  form  an  almost  dry  mass, 
not  readily  detachable  from  the  bottom  of  the  flask  by 
shaking,  is  dissolved  in  50  cc.  of  water  by  the  aid  of 


320      A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

gentle  heat.  When  solution  is  effected,  20  cc.  of  dilute 
sulphuric  acid  are  added.  This  decomposes  the  soap 
and  liberates  the  fat  acids. 

The  flask  is  then  connected  with  a  Liebig's  condenser 
and  the  contents  heated  to  moderate  boiling,  a  few 
small  pieces  of  glass,  broken  clay  pipe,  or  pumice-stone 
being  introduced  to  prevent  bumping. 

The  distillate,  which  contains  some  insoluble  acids, 
is  passed  through  a  small  wet  filter  as  it  drops  from 
the  condenser,  and  is  received  in  a  5o-cc.  measure. 

The  distillation  is  continued  until  exactly  50  cc.  has 
come  over.  This  distillate  contains  the  volatile  and 
soluble  fat  acids  of  the  butter  examined,  and  is  at  once 
titrated  with  decinormal  sodium-hydroxide  solution, 
using  phenolphthalein  as  an  indicator. 

When  thus  treated,  pure  butter  seldom  yields  less 
acidity  than  is  represented  by  12  cc.  of  decinormal 
soda.  When  butter  is  made  from  the  milk  of  a  single 
cow  it  sometimes  falls  to  11.5  cc. 

Reichert's  formula  for  determining  the  percentage 
of  butter-fat  in  mixed  fat  is 

B  =  ;.3(»  -  0.3), 

N 

n  being  the  number  of  cc.  of  —  alkali  used  in  neutral- 

10 

izing  the  distillate  from  2.5  gms.  of  the  fat. 

Oleomargarine  requires  only  0.8  to  0.9  cc.  of  alkali 
for  the  neutralization  of  the  distillate  from  2.5  gms; 
cacao  butter  requires  3.7  cc.  ;  lard, .0.6  cc. 

A  rapid  method  for  detecting  oleomargarine  or  an 
admixture  of  it  with  butter  is  to  heat  the  suspected 
substance  in  a  small  tin  dish  directly  over  a  gas  flame. 
If  it  melts  quietly,  foams,  and  runs  over  the  dish,  it  is 


A   TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       321 

butter ;    if  it  sputters   noisily  as  soon   as  heated   and 
foams  but  little,  it  is  oleomargarine. 

Another  way  is  to  heat  the  butter  for  a  moment 
with  an  alcoholic  solution  of  sodium  hydroxide  and 
then  empty  into  cold  water.  It  gives  a  distinct  odor 
of  pineapples  (due  to  ethyl  butyrate),  while  oleomar- 
garine gives  only  an  alcoholic  odor. 


322       A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 


CHAPTER   XXXIII. 
URINE. 

Normal  Urine  when  fresh  is  clear  and  transparent. 
Its  color  is  yellowish,  reddish,  or  colorless.  It  has  a 
peculiar  odor,  a  distinctly  acid  reaction,  and  its  average 
specific  gravity  is  from  1018  to  1022. 

On  standing  it  generally  gives  a  slight  cloud  of 
mucus,  which  slowly  sinks  to  the  bottom  ;  and  after 
heavy  exercise  or  a  hearty  meal  of  nitrogenous  food, 
a  sediment  of  urates. 

If  the  urine  be  very  dilute  and  the  temperature  is 
above  the  mean,  decomposition  rapidly  takes  place, 
and  the  urine  becomes  turbid,  acquires  an  alkaline  re- 
action, and  develops  a  nauseous  ammoniacal  odor. 

Reaction. — The  acid  reaction  of  fresh  urine  is  proba- 
bly due  to  the  presence  of  acid  phosphate  of  sodium. 
If  it  has  an  alkaline  reaction  when  first  voided  it  is 
probably  due  to  the  conversion  of  urea  into  ammo- 
nium carbonate  within  the  bladder ;  it  is  then  generally 
turbid,  and  indicates  an  abnormal  condition. 

The  reaction  is  best  tested  by  dropping  a  small  piece 
of  a  red  and  a  blue  litmus-paper  into  it.  If  both  are 
found  red  in  a  few  minutes  the  reaction  is  acid,  if  both 
are  blue  it  is  alkaline,  if  both  remain  unchanged  it  is 
neutral. 

Composition. — The  average  composition  of  healthy 
urine  is  as  follows: 


A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.      323 


Per  Cent. 

Grains  per  diem. 

Water  

06  oo 

50  fl    ozs. 

4.  OO 

icoo  grs 

Urea  

2.  SO 

CQO    " 

Uric  acid                                    .  .    . 

o  04 

9c  errs 

Hippuric  acid  .  .  •          .  .          .  .      . 

O   O7S 

T  C     O 

Creatinine     

O   O7S 

I  e    o 

Pigment,    mucus,    xanthine,  and    other 
extractives  

O    SO 

I  7O   O 

Chlorides  of  potassium  and  sodium...  . 

0.50 

170.0 

Sulphates  of  potassium  and  calcium.  .  . 

O.II 

40.0 

Phosphates  of  potassium  and  sodium. 

O.I2 

45.0 

Phosphates  of  magnesium  and  calcium. 

o.So 

35-5 

Beside  these  there  have  been  found  traces  of  indican, 
diastase,  glucose,  oxalic  acid,  lactic  acid,  carbolic  acid, 
and  unoxidized  sulphur  and  phosphorus.  (From 
"  The  Urine  ;  "  Holland.) 

The  composition  of  urine  is  not  constant :  it  is  influ- 
enced by  the  amount  of  water  and  other  fluids  taken, 
by  the  temperature  of  the  skin,  by  the  emotions,  the 
blood-pressure,  the  amount  of  work  done,  the  time  of 
day,  age,  sex,  and  medicine. 

The  Quantity  passed  in  24  hours  varies  considerably. 
The  average  quantity  passed  daily  by  a  healthy  adult 
is  1400  to  1600  cc. — about  50  fl.  ozs.  The  quantity  of 
total  solids  contained  in  this  is,  as  seen  in  the  table, 
about  60  gms.,  or  1000  grains.  About  one  half  of  these 
solids  is  composed  of  urea. 

In  making  an  analysis  of  urine  the  analyst  looks  for 
the  presence  of  abnormal  constituents,  and  determines 
the  excess  or  deficiency  of  the  normal  constituents  ;  and 
therefore,  since  the  composition  of  urine  is  not  the  same 
at  all  hours  of  the  day,  it  is  important  when  accurate 
results  are  desired  to  examine  a  portion  of  the  total 
quantity  of  the  urine  passed  in  twenty-four  hours.  If 


324      A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


this  cannot  easily  be  obtained,  or  only  a  casual  ex- 
amination is  to  be  made,  the  first  urine  passed  in  the 
morning  may  be  used. 

Specific  Gravity. — This  varies  from  1015  to  1028, 
according  to  the  degree  of  dilution  or  concentration. 
But  pathological  urine  may  vary  from  almost  that  of 
water  to  1050.  The  urine  of  Bright's  disease  is,  as  a 
rule,  of  low  specific  gravity,  and  in  diabetes  of  high 
specific  gravity. 

The    specific   gravity  may  be  taken  by  any  of  the 

usual  methods, 
but  the  urinom- 
eter  (a  special 
hydrometer ;  see 
Fig.  31)  is  gener- 
ally used  for  this 
purpose.  This 
instrument  is  usu- 
ally graduated  so 
that  only  the  last 
two  figures  of  the 
specific  gravity 
appear  upon  the 
stem,  and  so  as  to  read  correctly  at  60°  F.  If  the  tem- 
perature is  above  60°  F.  it  will  be  sufficiently  accurate 
for  ordinary  clinical  purposes  to  add  one  degree  in 
specific  gravity  for  every  10  degrees  of  temperature  ; 
that  is,  if  it  read  1018  at  80°  F.,  it  would  read  1020  at 
60°  F.,  or  for  every  i°  F.  above  60°  add  o.oooi  to  the 
observed  specific  gravity.  The  urinometer  is  used  as 
follows:  Sufficient  urine  is  placed  in  the  upright  jar  or 
cylinder  to  float  the  urinometer,  which  is  carefully 


FIG.  31. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       325 

introduced.  When  it  has  come  to  rest  bring  the  eye 
on  a  level  with  the  surface  of  the  liquid  in  the  jar,  and 
take  the  reading  at  the  lower  edge  of  the  meniscus 
formed  by  the  upper  surface  of  the  urine. 

The  mark  on  the  instrument  which  is  cut  by  this 
line,  and  which  can  be  distinctly  seen,  is  taken  as  t«he 
correct  reading. 

If  the  urine  be  turbid  this  method  cannot  be  em- 
ployed. 

After  taking  the  specific  gravity,  reaction,  etc.,  set  a 
portion  of  the  urine  aside  in  a  conical  glass  so  as  to 
allow  a  deposit  to  form,  which  must  be  examined 
microscopically  and  chemically,  as  described  later  on. 

Total  Solids. — The  total  solids  in  urine  may  be 
roughly  estimated  as  follows  : 

The  last  two  figures  of  the  specific  gravity  when 
multiplied  by  the  factor  2.33  will  give  the  number  of 
grammes  of  solid  matter  in  1000  cc.  of  the  urine. 

From  this  it  is  easy  to  calculate  the  quantity  of  solids 
passed  in  twenty-four  hours. 

If,  for  example,  1500  cc.  of  urine  were  passed  in 
twenty-four  hours,  and  the  specific  gravity  of  this  was 
1020,  the  total  solids  would  be  20  X  2.33  —  46.6  gms.  in 

1000  cc.     In  1500   cc.  there  will  be  — — ^—  =69.9 

10 

gms.  If  it  be  desired  to  use  the  English  measures,  we 
may  determine  the  total  solids  by  multiplying  the  last 
two  figures  of  the  specific  gravity  by  the  number  of 
fluid  ounces  of  urine  passed,  for  these  last  two  figures 
represent  approximately  the  grains  of  solid  matter  in  a 
fluid  ounce.  Thus  if  50  fluid  ounces  were  passed  and 
the  specific  gravity  is  1020,  the  total  solids  will  be 
50  X  20  =  1000  grs.  in  twenty-four  hours. 


326      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

A  more  exact  method  of  determining  the  total  solids 
is  to  evaporate  10  cc.  in  a  white  porcelain  dish  and  dry 
in  a  water-oven  to  a  constant  weight.  The  difference 
between  the  weight  of  the  dish,  and  of  the  dish  with 
the  solids  will  be  the  weight  of  the  solids  in  10  cc.  of 
urine.  Even  by  this  method  there  is  some  loss  through 
volatilization. 

Chlorides. — For  the  detection  of  chlorides  a  few 
drops  of  nitric  acid  are  added  to  the  urine  in  a  test- 
tube,  and  then  silver-nitrate  test  solution.  A  white, 
curdy  precipitate  of  silver  chloride  forms,  which  should 
occupy  not  more  than  one  fourth  the  volume  of  the 
urine  taken.  If  it  occupies  more,  the  chlorides  are  said 
to  be  increased  ;  if  it  occupies  less  space  than  one 
fourth,  the  chlorides  are  diminished.  It  is  always  ad- 
visable to  compare  the  specimen  under  examination 
with  normal  urine,  subjected  to  the  same  test.  In 
most  cases  such  an  approximate  result  is  all  that  is  re- 
quired in  a  clinical  examination. 

The  Volumetric  Estimation. — It  is  sometimes  neces- 
sary to  make  a  more  accurate  determination.  For  this 
purpose  a  decinormal  solution  of  silver  nitrate  is  used. 
10  cc.  of  the  urine  are  diluted  with  about  50  cc.  of 
water ;  a  few  drops  of  potassium  chromate  T.  S.  are 
added,  and  then  the  decinormal  silver  nitrate  V.  S.  run 
in  from  a  burette  until  a  permanent  reddish  color  is  pro- 
duced. Note  the  number  of  cc.  of  the  V.  S.  used,  and 
multiply  this  number  by  the  factor  for  chlorine,  0.00354 
gm.,the  factor  for  sodium  chloride,  or  0.00584  gm.  This 
will  give  the  quantity  of  chlorine  or  sodium  chloride  in 
10  cc.  of  urine.  This  when  multiplied  by  10  gives  the  per- 
centage. In  highly  colored  urines  this  method  is  some- 
times inapplicable,  because  the  change  of  color  is 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       327 

hidden  by  the  color  of  the  urine.  In  such  cases  Vol- 
hard's  method  (see  page  112)  may  be  employed. 

Phosphates.— Phosphoric  acid  exists  in  the  urine 
combined  with  the  alkalies  and  with  the  alkaline  earths. 
These  phosphates  are,  therefore,  generally  distinguished 
by  the  terms  alkaline  and  earthy  phosphates.  By 
adding  an  alkali  to  normal  urine  the  earthy  phosphates 
(calcium  and  magnesium)  are  precipitated. 

The  earthy  phosphates  may  be  approximately 
estimated  by  adding  a  few  drops  of  ammonia-water  to 
the  urine  and  observing  the  amount  of  turbidity  pro- 
duced after  boiling.  By  comparing  this  with  the 
amount  obtained  by  the  same  treatment  of  normal 
urine  the  excess  or  deficiency  is  determined.  The 
ppt.  is  Ca,(PO4)2  and  MgNH4PO4. 

The  alkaline  phosphates  may  be  detected  in  the 
filtrate  from  the  earthy  phosphates  by  the  addition  of 
a  few  drops  of  magnesium-sulphate  solution  and  some 
ammonium  chloride.  The  precipitate  will  be  much 
more  voluminous  than  that  produced  by  the  earthy 
phosphates,  and  the  excess  or  deficiency  may  be 
determined  by  comparison  with  normal  urine.  The 
precipitate  has  the  composition  MgNH4PO4. 

The  quantitative  estimation  of  the  phosphate  is 
rarely  required,  but  may  be  made  by  the  volumetric 
process  with  uranium  nitrate. 

Sulphates. — About  30  grains  or  2  grammes  of  sul- 
phates are  daily  discharged  in  the  urine. 

Test. — A  few  drops  of  hydrochloric  acid  are  added 
to  the  urine  in  a  test-tube  to  prevent  the  formation  of 
barium  phosphate.  Barium  chloride  T.  S.  is  now  added, 
which  causes  a  white  precipitate  in  the  presence  of 
sulphates.  This  should  be  compared  with  results 


$28      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

obtained  from  equal  quantities  of  healthy  urine  treated 
in  the  same  way. 

Volumetric  Estimation. — This  is  done  by  the  use  of 
a  standard  solution  of  barium  chloride. 

The  Gravimetric  Method. — Take  100  cc.  of  urine,  add 
5  cc.  HC1  and  heat  to  near  boiling,  then  add  barium 
chloride  T.  S.  in  slight  excess ;  place  the  beaker  con- 
taining the  mixture  on  a  water-bath  until  the  pre- 
cipitate has  subsided,  decant  the  clear  liquid  carefully 
from  the  precipitate,  add  hot  water,  and  when  the  pre- 
cipitate has  again  settled  decant  again  ;  continue  this 
until  the  decanted  liquid  no  longer  gives  a  cloudiness 
with  sulphuric  acid.  Then  dry  the  precipitate  and 
weigh  carefully.  This  gives  the  quantity  of  BaSO4 
which  is  precipitated  out  of  the  urine  by  barium 
chloride. 

207.7  parts  of  barium  sulphate  represent  98  parts  of 
sulphuric  acid.  Therefore  by  multiplying  the  weight 
obtained  by  98  and  dividing  by  207.7  tne  number  of 
grammes  of  sulphuric  acid  in  the  100  cc.  of  urine  taken 
is  obtained.  From  these  we  can  easily  calculate  the 
quantity  eliminated  in  twenty-four  hours. 

Total  Acidity. — Place  50  cc.  of  the  urine  in  a  beaker, 
add  3  or  4  drops  of  phenolphthalein,  and  then  run  into 
the  beaker  carefully  from  a  burette  decinormal  sodium 
hydroxide  V.  S.  until  a  faint  permanent  red  color 
appears.  The  number  of  cc.  of  the  decinormal  alkali 
used  multiplied  by  0.0063  gives  the  acidity  of  50  cc.  of 
the  urine,  expressed  in  grammes  of  oxalic  acid.  From 
this  the  total  acidity  is  determined  by  multiplying  by 
the  quantity  of  urine  passed  in  twenty-four  hours,  and 
dividing  by  50. 

If  the  urine  is  highly  colored  the  end    reaction   is 


A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.       329 

sometimes  difficult  to  see.  In  such  a  case  the  color 
may  be  removed  by  shaking  up  a  portion  of  the  urine 
with  coarsely  powdered  animal  charcoal,  then  filtering. 
The  urine  is  thus  decolorized,  and  the  pink  color  pro- 
duced by  the  indicator  at  the  completion  of  the  reaction 
is  easily  seen. 

Urea,  CO(NH,)2. — This  is  the  most  important  con- 
stituent of  the  urine,  as  it  is  the  chief  condition  in  which 
the  nitrogen  leaves  the  body.  It  may  be  detected  by 
evaporating  a  few  drops  of  urine  on  a  glass  slide, 
moistening  with  nitric  acid,  allowing  it  to  crystallize, 
and  examining  the  crystals  of  urea  nitrate  under  a 
microscope  of  low  power.  As  urea  is  generally  looked 
upon  as  an  index  of  the  retrograde  changes  going  on 
in  the  body,  or  of  the  eliminating  power  of  the  kidneys, 
its  quantitative  estimation  is  a  matter  of  great  import- 
ance. 

The  quantity  of  urea  eliminated  in  twenty-four  hours 
has  been  put  as  being  30  to  33  gms.,  or  from  430  to 
5  50  grains. 

The  Quantitive  Estimation  of  Urea  is  effected  by 
treating  it  with  alkaline  hypochlorites  or  hypobromites 
which  decompose  the  urea  into  CO2,  N,  and  HaO. 

Uric  Acid,  CBH4N4O3 ,  occurs  in  urine,  sometimes  in 
a  free  state,  but  oftener  in  combination  with  potassium, 
sodium,  or  ammonium,  and  occasionally  with  calcium 
and  magnesium.  These. are  called  urates.  It  is  de- 
tected microscopically,  and  varies  in  quantity  from  0.4 
to  0.8  gm.  (6  to  12  grs.)  in  twenty-four  hours.  The 
crystals  are  sometimes  large  enough  to  be  seen  by  the 
naked  eye.  It  deposits,  upon  standing,  in  the  form 
of  a  brick-colored  precipitate,  commonly  called  brick- 
dust. 


33O      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

Qualitative  Chemical  Tests. —  The  Murexid  Test. — A 
portion  of  the  urine  is  evaporated  to  dryness  in  a 
porcelain  dish  upon  a  water-bath.  The  residue  is 
then  moistened  with  nitric  acid,  and  after  evaporating 
off  the  nitric  acid  the  residue  is  moistened  with  am- 
monium hydroxide.  If  uric  acid  is  present  the  residue 
assumes  a  beautiful  purple-red  color,  due  to  the  forma- 
tion of  murexid. 

The  Silver-carbonate  Test. — Make  the  urine  alkaline 
with  Na2COs  or  KaCO3 ,  and  moisten  a  filter  paper  with 
the  liquid.  Now  touch  the  moistened  paper  with  a 
solution  of  AgNO3.  In  the  presence  of  uric  acid  a 
distinct  gray  stain  is  produced. 

Quantitative  Estimation  of  Uric  Acid. — Acidulate  a 
portion  of  the  urine  with  HC1,  and  set  aside  for  twenty- 
four  hours.  The  uric  acid  is  thus  set  free,  and,  being 
insoluble,  precipitates  and  adheres  to  the  bottom  and 
sides  of  the  vessel.  It  is  collected  on  a  weighed  filter, 
washed  thoroughly,  dried,  and  weighed.  The  heat 
used  should  not  be  over  100°  C.  (212°  F.).  The  weight 
of  the  filter  and  its  contents  minus  the  weight  of  the 
filter  alone  gives  the  weight  of  uric  acid  in  the  volume 
of  urine  taken.  The  quantity  eliminated  in  24  hours 
can  then  be  calculated. 


ABNORMAL  CONSTITUENTS. 

Albumen. — In  all  cases  the  urine  should  be  clear 
before  applying  the  tests  for  albumen.  If  not  clear,  it 
should  be  filtered. 

(a)  Boiling  -Test. — About  10  cc.  of  the  clear  urine  are 
placed  in  a  narrow  test-tube,  one  drop  of  acetic  or 
nitric  acid  is  added,  and  the  tube  heated  over  a  small 


A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS.       331 

flame  in  such  a  way  that  the  upper  portion  of  the 
liquid  only  will  be  heated.  In  the  presence  of  albumen 
the  urine  will  become  turbid,  more  or  less  so  in  propor- 
tion to  the  amount  of  albumen  present. 

If  the  acetic  or  nitric  acid  is  not  added  before  heat- 
ing, a  turbidity  will  be  produced  by  the  phosphates; 
this,  however,  will  again  disappear  upon  adding  the 
acid. 

(b)  The   Nitric-acid  Test. — About    2  cc.  of  pure  ni- 
tric acid   are    placed  in  a  test-tube,  and  the  tube  being 
inclined   to   one  side,  the  urine  is  carefully  run  down 
the  side  of  the  tube   so  that  it  will  float  upon  and  not 
mix  with  the  acid.     An  opaque-white  zone  will  appear 
at  the  line  of  contact  of  the  two  liquids,  if  albumen  is 
present. 

A  mixture  of  nitric  acicl  one  volume,  and  saturated 
solution  of  magnesium  sulphate  five  volumes,  is  some- 
times used  instead  of  pure  nitric  acid  in  the  above  test, 
and  is  used  in  the  same  way. 

(c)  Ferrocyanide-of -potassium   Test. — A  small  portion 
of  the  urine  is  acidulated   with  acetic  acid,  and  filtered 
if  much  of  a  precipitate  forms.     This  acidulated  urine 
is  then  floated  on  a  solution  of  potassium  ferrocyanide. 
A   white   precipitate    appears    if  albumen    is    present. 
This    is   a   very   delicate   and  reliable   test ;  peptone, 
mucin,  or  alkaloids  are  not  precipitated  by  it.     This  is 
known  as  Bodeker's  Test. 

(d)  Picric-acid    Test. — A     cold    saturated    solution 
of  picric   acid  may  be   used  in  the  same   way  as  the 
nitric  acid — by  contact.     A  white  zone  appears  at  the 
line  of  contact.    Alkaloids,  mucin,  peptones,  and  urates 
are,  however,  precipitated  as  well  as  albumen   in  this 


332       A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

test,  and  the   solution  should  be  heated  to  redissolve 
these. 

(e)  Sodium-tungstate     Test. — The    reagent    is    made 
by   mixing  equal    parts  of    a    cold  saturated  solution 
of    sodium-tungstate    and    citric-acid    solution.     This 
is  a  very  delicate  test,  and  is  applied  in  the  same  way 
as  the  nitric  acid  and  the  above.     Peptones,  alkaloids, 
mucin,  and  urates  are  also  precipitated  by  this  reagent, 
but  these  are  redissolved  upon  boiling. 

(f)  Potassio-mercuric-iodide  Test,  or  Tanrefs  Test. — 
The  reagent  is  prepared  as  follows :  Mercuric  chloride, 
1.35  gms.;  potassium  iodide,  3.3-2  gms.;  acetic  acid,  20 
cc.;  distilled  water,  80  cc.    The  two  salts  are  separately 
dissolved  in  water,  and  then  the  solutions  mixed   and 
the  acetic  acid  added.     This  solution   is  also  used  by 
the  contact   method.     It   is   very  delicate,  detecting   I 
part  of  albumen  in  20,000  parts  of  urine.     It  is  neces- 
sary to  heat  in  order  to  dissolve   the  alkaloids,  mucin, 
and  peptone,  which  are  precipitated  together  with  the 
albumen. 

(g)  Acidulated-brine  Test. — The  reagent  is  made  by 
adding  one  fluid  ounce  of  hydrochloric  acid  to  a  pint 
of  a  saturated  solution  of  common  salt  and  filtering. 

It  is  used  as  follows:  The  solution  is  heated  to  boil- 
ing, and  the  urine  added  by  the  contact  method.  A 
white  zone  appears  at  the  line  of  contact  if  albumen  is 
present.  Peptone,  alkaloids,  etc.,  are  not  precipitated 
by  this  reagent. 

The  Quantitative  Estimation  of  albumen  is  of  great 
importance,  but  comparative  tests  are,  as  a  rule,  suffi- 
cient. An  easy  comparative  test  is  to  heat  a  given 
quantity  of  urine  in  a  test-tube,  add  a  few  drops  of 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       333 

nitric  acid,  and  set  aside  for  about  twelve  hours,  and 
then   note  the  volume  occupied  by  the  pre- 
cipitated albumen.     This  is  generally  spoken 
of  as  volume  per  cent,  and  has  no  relation  to 
actual  percentage. 

More  accurate  results  are  obtained  with 
Esbach's  Albuminometer.  This  is  a  gradu- 
ated glass  tube  (Fig.  32).  Fill  the  tube  to  U 
with  the  urine,  then  to  R  with  the  reagent. 
Close  the  tube  with  a  rubber  stopper,  shake, 
and  set  aside  for  24  hours.  Then  note  the 
height  of  the  precipitate,  as  indicated  by  the 
graduations.  Each  of  the  numbered  divi- 
sions represents  a  gramme  of  albumen  in  1000 
cc.  of  urine.  The  reading  should  be  taken  FIG.  32. 
at  the  middle  of  the  albuminous  surface.  The  reagent : 
Picric  acid,  logms.;  citric  acid,  20  gms.;  water,  looogms. 

Blood. — A  small  quantity  of  the  urine  is  mixed  in  a 
test-tube  with  an  equal  volume  of  a  mixture  of  freshly 
prepared  tincture  of  guaiac  and  spirit  of  turpentine, 
which  has  been  exposed  to  the  air  for  some  time.  If 
blood-coloring  matter  is  present  the  mixture  assumes  an 
indigo-blue  color,  the  rapidity  of  formation  of  which 
depends  upon  the  amount  of  blood-coloring  matter 
present.  Pus,  saliva,  and  salts  of  iodine  also  give  a  blue 
color  with  this  test  ;  but  it  appears  only  after  a  con- 
siderable lapse  of  time,  and  is  seldom  likely  to  mislead. 
Instead  of  the  spirit  of  turpentine,  peroxide  of  hydro- 
gen may  be  used. 

Pus. — The  presence  of  pus  is  easily  revealed  by  the 
microscope. 

Urine  containing  pus  is  always  turbid  to  the  naked 
eye,  and  deposits  a  white  or  greenish-white  sediment, 


334       A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 

which  resembles  urates  or  earthy  phosphates.  If 
heated  the  sediment  does  not  disappear — difference 
from  urates,  neither  is  it  dissolved  by  dilute  acids — 
difference  from  earthy  phosphates.  It  dissolves,  how- 
ever, in  strongly  alkaline  solutions,  giving  a  gelatinous, 
ropy  liquid.  Pus  effervesces  with  hydrogen  peroxide. 

Sugar. — (a)  Bismuth  Test. — A  few  cc.  of  urine  are 
placed  in  a  test-tube,  and  an  equal  volume  of  sodium- 
hydroxide  solution  and  a  little  bismuth  subnitrate  ; 
mix  well,  and  boil  for  a  few  minutes.  A  black  precipi- 
tate is  produced  if  sugar  is  present. 

If  albumen  is  present  it  must  be  removed  before  ap- 
plying the  test,  as  it  is  decomposed  by  boiling  with  the 
alkali,  forming  a  black  sulphide  of  bismuth. 

(b)  Nylanders   Test  is  a  modification  of  the  above. 
A  solution  is  made  of  bismuth  subnitrate  2  gms.,  Ro- 
chelle  salt  4  gm.,  sodium  hydroxide  8  gms.,  and  dis- 
tilled water  100  cc. 

Heat  the  urine  to  boiling,  and  add  a  few  drops  of 
this  alkaline  solution  of  bismuth,  continuing  the  boil- 
ing. If  sugar  is  present,  the  mixture  turns  black. 

This  is  a  very  delicate  test,  but  as  in  the  previous 
one,  any  albumen  must  be  removed. 

(c)  Moore's    Test. — Add  one  part  of  liquor  soda  to 
two  parts  of  urine,  and  boil.     If  sugar  is  present  the 
urine  will  become  blackish  brown.     Albumen  must  be 
removed  before  applying  the  test. 

(d)  Picric-acid  Test. — About   5  cc.  of  the  urine  are 
mixed  with  half  as  much  of  picric-acid  solution   and 
about  2  cc.  of  liquor  potassa,  and  boiled.    A  dark  mahog- 
any-red color  is  developed  in  the   presence  of  sugar. 
Albumen  will  cause  turbidity,  but  will   not   interfere 
with  the  test. 


A   TEXT-BOOK    OF  VOLUMETRIC   ANALYSIS.       335 

(e)  Trommers  Test. — 5  cc.  of  urine  are  mixed  in  a 
test-tube  with  one  half  of  its  volume  of  liquor  soda, 
and  one  or  two  drops  of  a  solution  of  CuSO4  (i-io). 
In  the  presence  of  sugar  a  clear,  deep-blue  color  is  ob- 
tained. Heat  the  solution  now  almost,  though  not 
quite,  to  boiling.  At  first  a  greenish  then  a  yellow 
turbidity  forms,  which  rapidly  changes  to  a  reddish- 
yellow  color,  and  precipitates  red  cuprous  oxide.  An 
excess  of  the  copper  solution  should  not  be  used. 

(/)  Haines  Test. — The  reagent  used  is  a  solution  of 
copper  sulphate  in  a  mixture  of  equal  parts  of  glyce- 
rine and  water. 

To  about  5  cc.  of  urine  add  a  few  drops  of  this  re- 
agent, and  then  add  sodium-hydroxide  solution  until 
the  liquid  assumes  a  deep-blue  color.  The  mixture  is 
then  gradually  heated  to  boiling.  If  sugar  is  present 
the  color  changes  to  yellow,  and  finally  brick-red. 

Or)  Indigo-carmine  Test. — The  reagent  is  made  by 
mixing  I  part  of  dried  commercial  extract  of  indigo 
with  30  parts  of  pure  dry  sodium  carbonate. 

The  test :  Add  enough  of  this  powder  to  5  cc.  of 
the  urine  to  give  it  a  transparent-blue  color,  and  heat 
to  boiling.  If  sugar  is  present,  the  color  changes  to 
violet,  cherry-red,  and  finally  yellow.  On  gently  agi- 
tating the  tube  the  colors  appear  in  the  reversed  order. 

(/i)  Molisctis  Test. — Put  I  cc.  of  the  urine  in  a  test- 
tube,  add  2  cc.  of  a  saturated  solution  of  alpha-naph- 
thol,  mix  well,  and  then  add  an  excess  of  sulphuric  acid. 
A  deep  violet  color  is  produced  if  sugar  is  present.  On 
dilution  with  water  a  blue  ppt.  occurs. 

Thymol  or  menthol  may  be  used  instead  of  naph- 
thol.  The  color  then  produced  is  deep  red. 

Quantitative  Estimation. — This  is  generally  effected 


33^       A   TEXT-BOOK    OF  VOLUMETRIC   ANALYSIS. 

by  the  use  of  Fehling's  solution.  The  process  is  de- 
scribed on  page  259. 

By  Fermentation. — This  is  performed  by  adding  a 
small  quantity  of  yeast  to  a  certain  volume  of  urine 
and  setting  aside  for  about  24  hours.  As  the  sugar  is 
decomposed  the  specific  gravity  of  the  urine  becomes 
less.  Therefore  by  taking  the  specific  gravity  of  the 
urine  before  and  after  fermentation  a  fairly  accurate 
estimation  of  the  sugar  present  may  be  made,  provided 
the  quantity  be  not  less  than  0.5  per  cent.  Each  de- 
gree of  the  urinometer  indicates  0.219  Per  cent,  of  sugar. 
If  the  specific  gravity  of  a  sample  of  urine  is  found  to 
be  1032,  and  after  subjecting  it  to  fermentation  it  is 
1022,  the  quantity  of  sugar  present  in  the  sample  is  10 
times  0.219  =  2.19$. 

Estimation  of  Sugar  by  Dr.  Einhorn's  Fermen- 
tation Saccharometer. — Take  one  gramme  of  com- 
mercial compressed  yeast  (or  -fa  of  a  cake  of  Fleisch- 
mann's  yeast),  shake  thoroughly  in  the  graduated 
test-tube  with  10  cc.  of  the  urine  to  be  examined. 
Then  pour  the  mixture  into  the  bulb  of  the  saccharom- 
eter  (Fig.  33).  By  inclining  the  apparatus  the  mix- 
ture will  easily  flow  into  the  cylinder,  thereby  forcing 
out  the  air.  Owing  to  the  atmospheric  pressure  the 
fluid  does  not  flow  back,  but  remains  there. 

The  apparatus  is  to  be  left  undisturbed  for  twenty  to 
twenty-four  hours  in  a  room  of  ordinary  temperature. 

If  the  urine  contains  sugar,  the  alcoholic  fermenta- 
tion begins  in  about  twenty  to  thirty  minutes.  The 
evolved  carbonic-acid  gas  gathers  at  the  top  of  the 
cylinder,  forcing  the  fluid  back  into  the  bulb. 

On  the  following  day  the  upper  part  of  the  cylinder 
is  filled  with  carbonic-acid  gas.  The  changed  level  of 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       337 

the  fluid  in  the  cylinder  shows  that  the  reaction  has 
taken  place,  and  indicates  by  the  numbers — to  which 
it  corresponds — the  approximate  quantity  of  sugar 
present. 

If   the  urine  contains  more  than  one   per  cent  of 


FIG.  33. 

sugar,  then  it  must  be  diluted  with  water  before  being 
tested. 

Diabetic  urines  of  straw  color  and  a  specific  gravity 
of  1018-1022  may  be  diluted  twice  ;  of  1022-1028,  five 
times  ;  1028-1038,  ten  times. 

The  original  (not  diluted)  urine  contains  in  propor- 
tion to  the  dilution  two,  five,  or  ten  times  more  sugar 
than  the  diluted  urine. 


338       A  TEXT-BOOK    OF   VOLUMETRIC   ANALYSIS. 

In  carrying  out  the  fermentation  test  it  is  always 
recommendable  to  take,  besides  the  urine  to  be  tested, 
a  normal  one,  and  to  make  the  same  fermentation  with 
it. 

The  mixture  of  the  normal  urine  with  yeast  will 
have  on  the  following  day  only  a  small  bubble  on  the 
top  of  the  cylinder.  That  proves  at  once  the  efficacy 
and  purity  of  the  yeast. 

If  there  is  likewise  in  the  suspected  urine  a  small 
bubble  on  the  top  of  the  cylinder,  then  no  sugar  is 
present ;  but  if  there  is  a  much  larger  gas  volume,  then 
we  are  sure  that  the  urine  contains  sugar. 

Test  for  Bile. — (a)  Oliver  s  Test. — Dissolve  2  gms. 
of  fresh  peptone  (Savory  &  Moore's  Pulverized),  0.25 
gm.  salicylic  acid,  and  2  cc.  of  33$  acetic  acid  in  water 
to  make  200  cc.  The  solution  should  be  rendered 
perfectly  clear  by  filtration. 

The  urine  should  also  be  clarified  by  filtration,  and 
diluted  to  a  specific  gravity  of  1008.  One  cc.  of  this 
urine  is  added  to  3  cc.  of  the  above  reagent.  If  bil- 
iary salts  are  present  a  distinct  opalescence  at  once 
appears,  which  becomes  more  intense  in  about  five 
minutes.  This  opalescence  will  be  more  or  less  dis- 
tinct in  proportion  to  the  quantity  of  bile  present. 

(b)  Gmelins  Test. — 2  or  3  cc.  of  partially  decomposed 
yellow  nitric    acid   are  placed   in  a  test-tube,  and   an 
equal   volume    of   the    urine  is   cautiously  poured    on 
top.     In  the  presence  of  bile  pigments  a  play  of  colors 
will  appear,  beginning  with  green,  then  passing  through 
blue,  violet,  red,  and  yellow. 

The  nitric  acid  may  be  prepared  for  this  test  by 
adding  a  fragment  of  zinc  to  ordinary  nitric  acid. 

(c)  Pettenkofers  Test. — Mix  equal  parts  of  urine  and 


A   TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS.       339 

sulphuric  acid,  add  one  drop  of  simple  syrup,  and  apply 
a  gentle  heat.  The  color  will  change  from  cherry-red 
to  purple  if  biliary  acids  are  present. 

(<-/)  Ultzmanns  Test. — 5  cc.  of  urine  are  mixed  with 
2  cc,  of  a  strong  solution  of  KOH  (1-3)  and  then  an 
excess  of  pure  HC1  added.  The  mixture  will  become 
emerald-green  if  biliary  pigments  are  present. 

(e)  Tincture- of -iodine  Test. — A  few  drops  of  iodine 
tincture  are  floated  upon  the  surface  of  the  urine.  If 
biliary  pigments  are  present,  there  will  appear  at  the 
line  of  contact  of  the  two  liquids,  after  a  few  minutes, 
a  beautiful  emerald-green  zone. 


URINARY   DEPOSITS. 

Chemical  Examination.— Draw  off  a  portion  of  the 
sediment  with  a  pipette  or  glass  tube,  and  transfer  to  a 
watch-glass  or  small  test-tube. 


White 


f  Dissolves  on  heating  urine. ... Ammonium  urate. 

f  Sol.  in  NH4OH Cystine. 

f  Soluble  in  acetic  acid, 
Jeposit.    .  Earthy  Phosphates. 

*n  {   Insol.inNH4OH,  •{  Insoluble    in     acetic 
neatinfir.  .,      ,^  y  . 

acid,    Calcium    oxa- 

[     late  or  oxalurate. 
I.  Gelatinizes  in  NH4OH..  .Pus  (see  above). 

f  Visibly  crystalline  (red) Uric  acid. 

£  |        ,     I  f  Pale,  easily  soluble  by  heat Urates. 

n  n  ^J    Amor-  J   Deep  colored,  slowly  soluble  by  heat,  Acidurates 

\   phous.   I       w/M  uroerythrin. 
t.  i.  Red,  insoluble  by  heat,  alkalies  or  acids.  .Blood. 

Microscopical  Examination.— With  a  clean  pipette 
draw  off  a  small  portion  of  the  sediment,  transfer  to  a 
clean  glass  slide,  and  examine  with  a  ^-in.  or  |--in.  ob- 
jective. A  cover  glass  may  be  dispensed  with. 


340      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


f  Small  granules  with  spicules  on 

larger  granules (  light  =  Sodium  urate. 

Deposit   I  Vanishes    on    adding    KOH   or-! 
is  Amor-^       NaOH (dark 


phous. 


De- 
posit 

is 

Crys- 
tal- 
line. 


' 


Ammonium  urate. 
Permanent,    adding    KOH 

NaOH Calcium  phosphate  (rare). 

Globules,  strongly  refracting  light Fat. 

( Reddish,   cross,  or   whetstone  shape, 

or  in  groups Uric  acid. 

Regular  octahedra,  envelope-shaped,  Caldiim  oxalate. 
Hexagonal  plates,  soluble  in  NH4OH 

(white) Cystine. 

Bundles    of    needles    crossing    each 

(^      other Tyrosin. 

{  Large    prisms,    soluble    in    acetic    acid    (coffin-lid 

I       shape),  Amman,  magnesium  phosphate. 
Brown,  double  spheres,  spiculated,   Urate  of  ammo- 
nium. 
Club-shaped  crystals,  single  or  in  groups,  Calcium 

phosphate. 

Double  spheres,  radiated  structure,  soluble  in  acetic 
acid,  with  effervescence,  Calcium  carbonate 
(rare). 

Double  spheres,  insoluble  in  acetic  acid,  Calcium 
oxalurate  (rare). 

(  Double  spheres,  yellow  or  red,  radiated Uric  acid. 

Red  or  yellow  disks,  biconcave  ;   sometimes  irregular  in  out- 
line, Blood  cells. 


Alkaline 
Urine. 


Cellu- 
lar 
Ele- 
ments. 


corPusdes 


Albumen  present  ............  Pus. 


Round,  conical,  or  flat  cells  with  one  nucleus,  Epithelium  from 

urinary  tract. 
Tadpole-shape,  with  long  tail  ..................  Spermatozoa. 

Cylinders,    parallel   margins,   clear,   granular,  or  containing 

epithelial  cells  as  blood  cells.  ..Casts  of  uriniferous  tubules. 
Fungi,  yeast,  hairs,  threads,  etc.,  etc.  .  .  .Extraneous  matters. 
—  From  Hartley1  s  Medical  Chemistry. 


A  little  experience  in  the  microscopical  examination 
of  urinary  sediments  will  usually  enable  one  to  readily 
recognize  the  various  forms,  and  thus  obviate  the  neces- 
sity for  a  chemical  examination. 


PART  III. 

GA  SOME  TRIG  ANAL  YSIS. 


CHAPTER  XXXIV. 
THE  NITROMETER. 

FOR  general  gas  analysis,  and  for  the  rapid  estima- 
tion of  such  substances  as  ethyl  nitrite,  hydrogen 
peroxide,  urea,  bleaching-powder,  manganese  peroxide, 
etc.,  an  instrument  called  the  nitrometer  is  used. 

The  apparatus  in  its  simplest  form  is  shown  in  Fig. 
34.  It  consists  of  a  measuring-tube  (A) 
graduated  in  cc.,  and  fitted  at  the  top 
with  a  three-way  stop-cock  (D)  and  a 
glass  cup  or  funnel  (C).  The  stop-cock 
is  so  arranged  that  according  to  the 
way  in  which  it  is  turned  it  will  dis- 
charge the  contents  of  the  cup  either 
into  the  tube  below  or  out  in  the  waste- 
opening  (E) ;  or  it  will  discharge  the 
contents  of  the  graduated  tube  into 
the  waste-opening. 

The  graduated  tube  generally  has  a 
capacity  of  50  cc.,  and  is  graduated  in 
-^  cc.,  the  graduation  beginning  at  the  top.  This 
measuring-tube  is  connected  by  means  of  a  strong 

342 


FIG.  34. 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       343 

flexible  india-rubber  tube  with  an  ungraduated  tube 
(B)  called  the  control-tube,  pressure-tube,  or  level-tube. 
Both  tubes  are  held  in  clamps  upon  a  stand. 

With  this  apparatus  gases  can  be  rapidly  and  accu- 
rately measured  at  definite  temperature  and  pressure. 

In  measuring  the  gas  the  instrument  is  filled  with 
some  liquid  in  which  the  gas  is  insoluble — generally 
mercury.  In  many  cases  a  saturated  solution  of  salt 
may  be  used. 

Suppose  we  fill  the  instrument  with  mercury  in  such 
quantity  that  when  the  stop-cock  is  opened  and  the 
control-tube  raised,  the  mercury  will  rise  as  far  as  the 
top,  and  about  two  inches  in  the  control-tube. 

The  top  is  now  closed,  the  control-tube  lowered, 
and  a  little  carbonic-acid  gas  admitted  through  (E). 
The  top  is  then  again  closed,  and  the  instrument  al- 
lowed to  stand  until  its  contents  have  acquired  the 
temperature  of  the  room.  A  centigrade  thermometer 
suspended  to  the  stand  will  then  give  the  temperature 
of  the  gas. 

The  control-tube  is  now  raised  or  lowered  so  as  to 
make  the  level  of  the  liquid  in  both  tubes  the  same. 
This  makes  the  pressure  in  the  tube  the  same  as  the 
atmospheric  pressure  outside,  and  by  referring  to  a 
barometer  standing  near  this  pressure  is  ascertained. 

We  now  have  a  definite  volume  of  the  gas  at  a 
known  temperature  and  pressure. 

It  now  only  remains  to  read  off  the  volume  of  the 
gas,  and  correct  it  to  the  normal  temperature  and 
pressure  by  Charles'  and  Boyle's  laws,  respectively. 

The  normal  temperature  and  pressure  is  o°  C.  and 
760  mm.  pressure. 

The  weight  of  the  gas  in  grammes  may  then  be  cal- 


344      A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

culated  from  its  volume  by  multiplying  the  number  of 
cc.  at  the  normal  temperature  and  pressure,  by  the 
weight  of  one  cc.  of  the  gas  in  grammes.  . 

This  weight  may  be  found  as  follows: 

1000  cc.  of  hydrogen  at  normal  temperature  and 
pressure  weigh  0.0896  gm.  One  cc.  of  H  then  weighs 
0.0000896  gm. 

One  cc.  of  oxygen  weighs  16  times  as  much,  and  one 
cc.  of  nitrogen  weighs  14  times  as  much.  Therefore, 
by  multiplying  the  weight  of  one  cc.  of  H  by  the 
atomic  weight  of  an  elementary  gas,  or  half  the  molec- 
ular weight  of  a  compound  gas,  the  weight  of  one  cc. 
of  that  gas  is  obtained. 

According  to  the  law  of  Charles,  the  volume  of  a 
gas  under  constant  pressure  varies  directly  with  the  ab- 
solute temperature. 

All  gases  expand  or  contract  by  y^  of  their  volume 
for  each  centigrade  degree  of  temperature,  increased 
or  decreased. 

We  may  regard  a  gas  at  o°  C.  as  having  passed 
through  273°  C.  In  other  words,  273°  below  zero  must 
be  regarded  as  the  absolute  zero,  and  o°  C.  as  273°  ab- 
solute temperature. 

Thus  the  absolute  temperature  centigrade  is  the  ob- 
served temperature  -)-  273°. 

Example. — A  given  volume  of  oxygen  gas  at  15°  C. 
measures  20  cc.  What  will  it  measure  at  o°  C.  ? 

X2o  =  ^ 

288° 

Boyle's  Law. — The  volume  of  a  confined  gas  is  in- 
versely proportional  to  the  pressure  brought  to  bear 
upon  it.  That  is,  the  less  the  pressure  the  greater  the 
volume,  and  vice  versa. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.      34$ 

Rule.  —  Multiply  the  observed  volume  by  the  observed 
pressure,  and  divide  by  the  normal  pressure. 

Example.  —  A  given  volume  of  gas  at  750  mm.  press- 
ure measures  20  cc.  What  will  it  measure  at  760  mm. 
(the  normal  pressure)? 

750  X  20  cc. 

=  I9'73  CC'     Ans' 


Now  let  us  take  an  example  in  which  both  laws  are 
involved. 

A  given  volume  of  oxygen  at  15°  C.  subjected  to  a 
pressure  of  750  mm.  measures  20  cc.  What  will  it 
measure  at  the  normal  temperature  and  pressure?  — 
i.e.,  o°  C.  and  760  mm. 

In  the  first  example  we  find  that  20  cc.  of  oxygen  at 
15°  C.  will  measure  at  o°  C.  18.95  cc.  Then 

750  X  18.95  cc. 

~*'      -  =  18.70  cc.     Ans. 

Now  to  find  the  weight  of  this  volume  of  oxygen  we 
proceed  as  follows: 

i  cc.  of  H  weighs  0.0000896  gm.  ; 

i  cc.  of  O  weighs  16  X  .0000896  =  0.0014336  gm.  ; 

18.700:.  of  O=  1  8.  70X0.0014336  gm.,  or  0.02680832  gm. 


346      A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS. 


CHAPTER   XXXV. 
ASSAY  OF  SPIRITUS  ^ETHERIS  NITROSI. 

Spirit  of  Nitrous  Ether. — This  is  an  alcoholic  solu- 
tion of  ethyl  nitrite  (C,H6NO3  =  74.97),  yielding  when 
freshly  prepared  and  tested  in  the  nitrometer  not  less 
than  ii  times  its  own  volume  of  nitrogen  dioxide 
(NO  =  29.97),  U.  S.  P. 

When  nitrites  are  mixed  with  an  excess  of  KI  and 
acidulated  with  H2SO4,  iodine  is  liberated,  and  all  the 
nitrogen  of  the  nitrite  is  evolved  in  the  form  of  NO,  as 
shown  in  the  equation 

2C,H6NOa  +  2KI  +  2H2S04 

149-74  =  2C3H6OH  +  2KHSO,  +  I2  +  2NO. 

59-94 

The  process  of  the  U.  S.  P.  is  conducted  as  follows : 
Open  the  stop-cock  of  the  measuring-tube,  raise  the 
control-tube,  and  pour  into  the  latter  a  saturated  solu- 
tion of  NaCl  until  the  measuring-tube,  including  the 
bore  of  the  stop-cock,  is  completely  filled,  Then  close 
the  stop-cock  and  fix  the  control-tube  at  a  lower  level. 
Now  introduce  into  the  funnel  at  the  top  of  the  meas- 
uring-tube 5  cc.  of  recently  prepared  spirit  of  nitrous 
ether,  open  the  stop-cock,  and  allow  the  spirit  to  run 
into  the  nitrometer,  being  careful  that  no  air  enters  at 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       347 

the  same  time.  10  cc.  of  potassium  iodide  T.  S.  are 
now  added  in  the  same  manner,  and  followed  by  10  cc. 
of  normal  sulphuric  acid  V.  S.  Effervescence  takes 
place  immediately,  and  if  the  tube  be  vigorously  shaken 
at  intervals  the  reaction  will  complete  itself  in  ten 
minutes.  The  control-tube  is  now  lowered  so  as  to 
make  the  level  of  the  liquid  in  both  tubes  the  same, 
and  the  volume  of  the  gas  in  the  graduated  tube  read 
off. 

According  to  the  U.  S.  P.,  the  volume  of  NO  gener- 
ated at  the  ordinary  indoor  temperature  (assumed  to  be 
at  or  near  25°  C,  77°  F.)  should  not  be  less  than  55  cc.  if 
5  cc.  of  the  spirit  are  taken,  corresponding  to  about  4 
per  cent,  of  pure  ethyl  nitrite. 

Sodium-chloride  solution  is  used  in  the  above  assay, 
because  owing  to  its  density  the  spirit  will  float  on  top, 
and  the  gas  evolved  will  not  dissolve  in  it.  At  the 
same  time  the  expense  of  using  mercury  is  saved.  It 
is  important  that  no  air  be  allowed  to  get  into  the 
measuring-tube,  because  this  would  convert  the  NO 
into  a  higher  oxide  of  nitrogen,  which  would  dissolve 
in  the  salt  solution,  and  thus  vitiate  the  result. 

If  it  is  desired  to  ascertain  the  percentage  of  ethyl 
nitrite  present  in  a  sample  of  spirit  of  nitrous  ether 
which  is  either  above  or  below  the  U.  S.  P.  standard, 
it  is  necessary  to  find  how  much  ethyl  nitrite  each  cc. 
of  NO  represents,  under  a  definite  degree  of  tempera- 
ture and  pressure. 

It  is  generally  convenient  to  correct  the  volume  of 
gas  evolved  at  higher  temperatures  to  its  correspond- 
ing volume  at  o°  C. 

The  calculations  involved  are  fully  explained  below. 

Example. — 5  cc.  of  spirit  of  nitrous  ether  (sp.  gr.  0.840) 


348       A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

are  treated  in  a  nitrometer,  and  the  NO  evolved  meas- 
ures 55  cc. 

The  temperature  at  which  the  operation  is  conducted 
is  25°  C.,  and  the  atmospheric  pressure  normal. 

What  per-cent.  of  ethyl  nitrite  is  present  in  the 
sample  ? 

By  consulting  the  equation  given  above,  it  will  be 
seen  that  one  molecular  weight  of  NO  —  29.97  is 
evolved  from  one  molecular  weight  of  ethyl  nitrite, 
74.87. 

Now  reduce  the  volume  of  the  gas  liberated  at  25°  C. 
to  its  corresponding  volume  at  o°  C.  Thus 

273°  +  25°  :  55  :  :  273°  +  o°  :  x.     x  =  50.4  cc. 

Thus  the  gas  evolved  from  5  cc.  of  the  spiritus  aetheris 
nitrosi,  measured  at  o°  C.,  is  50.4  cc. 

The  next  step  in  the  calculation  is  to  find  how  much 
ethyl  nitrite  each  cc.  of  the  evolved  NO  represents. 
One  litre  of  hydrogen  at  o°  C.  and  normal  pressure 
weighs  0.0896  gm. 

By  multiplying  this  weight  by  half  the  molecular 
weight  of  NO,  the  weight  of  1000  cc.  of  the  latter  gas 
is  obtained  ;  this  will  be  found  to  be  1.3423.  Now  if 
I»3423  £m-  °f  NO  measures  1000  cc.,  29.97  gms.  will 
measure  22328.24  cc. 

1.3423  :  IOOO  :  :  29.97  :  x.     x  =  22328.24. 

Then  if  22328.24  cc.  of  NO  are  evolved  by,  and  con- 
sequently represent,  74.87  gms.  of  ethyl  nitrite,  as  the 
equation  shows,  I  cc.  of  NO  will  represent  0.0033529 
gm.  of  pure  ethyl  nitrite. 

Now,  since  in  the  above  example  50.4  cc.  of  gas  were 


mm 

es*" 


A   TEXT-BOOK   OF   VOLUMETRIC    ANALYSIS.       349 

evolved   at  o°  C,  the   5   cc.  of   spirit  of  nitrous  ether 
examined  must  contain 

50.4  X  0.0033529  gm.  =  0.1689912  gm. 

of  pure  ethyl  nitrite. 

In  order  to  determine  the  percentage  strength,  the 
weight  of  the  spirit  taken  must  be  known.  This  may 
be  found  by  multiplying  the  measure  by  the  specific 
gravity,  5  cc.  X  0.840  —  4.2  gms.  Then 

4.2  gms.  :  0.1689912  gm.  :  :  100  :  x.     x  =  4$. 

at    °°  C'  and  ?6°  mm.  =1.3423  gms., 


r  XT^ 

N0      at  25°  C.,  and  760  mm.  =  1.2297  gms. 

I  cc.  of  NO  is  the  equivalent  of  —  - 

At  o°  C.  At  25°  C. 

Amyl  nitrite,  C6HnNO3.  .  ,  .  0.0052305  0.0047923  gm. 

Ethyl  nitrite,  C2H5NO2.  .  .    .0.0033529  0.0030716    " 

Sodium  nitrite,  NaNO2  ____  0.0030873  0.0028283    " 

Amyl  Nitrite  is  a  liquid  containing  about  80  per 
cent,  of  amyl  nitrite  (principally  iso  -  amyl  nitrite), 
C5HnNOa  —  1  16.78,  together  with  variable  quantities 
of  undetermined  compounds. 

The  U.  S.  P.  assay  is  as  follows  :  0.26  gm.  of  amyl 
nitrite  are  diluted  with  5  cc.  of  alcohol,  introduced  into 
the  nitrometer  as  directed  for  spiritus  aetheris  nitrosi  ; 

N 
10  cc.  of  potassium  iodide  T.  S.  and  10  cc.  of  --  H2SO4 

V.  S.  are  then  added  ;  and  the  volume  of  NO  gener- 
ated, measured  at  the  ordinary  indoor  temperature 
(assumed  to  be  at  or  near  25°  C.  or  77°  F.),  should  be 
about  40  cc.  Each  cc.  at  this  temperature  represents 
0.004792  gm.  of  pure  amyl  nitrite,  or  about  2  per  cent. 


35O      A   TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

Sodium  Nitrite,  NaNO2  =  {  ^8*93.—  This,  like  the 

(    °9 

other  nitrites  mentioned,  when  treated  with  potassium 
iodide  and  sulphuric  acid,  is  decomposed,  and  NO  is 
given  off. 

The  reaction  is  here  illustrated  : 


=  KaSO4  +  Na2SO4  +  2H2O  +  2NO  +  I2. 

A  molecule  of  NaNO2  (68.93)  evolves,  when  properly 
treated,  one  molecule  of  NO  (29.97). 

The  U.  S.  P.  assay  process  is  as  follows  :  Weigh  out 
0.15  gm.  of  NaNO2,  dissolve  it  in  about  5  cc.  of  water, 
and  introduce  the  solution  into  a  nitrometer.  This  is 
followed  by  a  solution  of  I  gm.  of  KI  in  6  cc.  of  water 

N 
and   15  cc.  of  —  -  H2SO4.     The  gas  which  is  liberated 

should  measure  not  less  than  50  cc.  at  15°  C.  (59°  F.) 
or  51.7  cc.  at  25°  C.  (77°  F.),  corresponding  to  not  less 
than  97.6  per  cent  of  the  pure  salt.  Each  cc.  at  25°  C. 
represents  0.0028283  gm.  and  at  o°  C.  0.0030873  gm., 
of  pure  NaNO2. 

ESTIMATION   OF  NITRIC  ACID   IN  NITRATES. 

This  may  also  be  effected  by  the  use  of  the  nitrom- 
eter. 

When  a  nitrate  is  shaken  up  with  an  excess  of  sul- 
phuric acid  and  mercury,  the  nitrate  is  decomposed 
and  NO  is  evolved,  as  seen  in  the  following  equation  : 


2)202  =  3HgS04  +  K2S04  +  2NO 

ioi  2)59.94 

29.97 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       351 

Thus  each  molecule  of  the  nitrate  radical  NO,  gives 
off  a  molecule  of  NO. 

Not  more  than  0.2  gm.  of  nitrate  should  be  taken 
for  analysis,  since,  if  this  quantity  is  exceeded,  the 
volume  of  gas  evolved  will  be  greater  than  the  in- 
strument can  conveniently  hold.  In  this  estimation 
the  nitrometer  is  filled  with  mercury  instead  of  brine ; 
the  nitrate  is  dissolved  in  5  cc.  of  water,  introduced 
into  the  nitrometer,  and  followed  by  excess  of  strong 
sulphuric  acid.  The  instrument  is  well  shaken  for 
some  time,  and  when  action  has  ceased  and  the  con- 
tents have  cooled  down  to  the  temperature  of  the 
room,  the  level  is  adjusted  and  the  volume  of  NO  read 
off  and  calculated  in  the  usual  way. 


352      A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 


CHAPTER   XXXVI. 

ESTIMATION   OF   SOLUBLE   CARBONATES   BY   THE 
USE   OF   THE   NITROMETER. 

THE  nitrometer  may  be  used  for  estimating  am- 
monium carbonate  in  aromatic  spirit  of  ammonia. 

The  nitrometer  in  this  case  must  be  charged  with 
mercury,  as  the  liberated  CO3  is  soluble  in  aqueous 
liquids. 

A  given  volume  of  the  spirit  is  introduced  into  the 
nitrometer,  followed  by  an  excess  of  dilute  HC1,  and 
the  evolved  gas  then  read  off ;  and  from  its  quantity 
the  proportion  of  ammonium  carbonate  may  be  calcu- 
lated by  applying  the  equation 

(NH4)9CO,+  2HC1  =  2NH4C1  +  H.O+  CO,. 

*96  *44 

The  volume  of  gas  liberated  must  first  be  reduced 
to  its  corresponding  volume  at  o°  C. 

Each  cc.  of  COa  at  o°  C.  weighs  0.001966  gm.  Now 
if  44  gms.  of  COa  represent  96  gms.  of  normal  am- 
monium carbonate,  how  much  ammonium  carbonate 
does  0.001966  gm.  of  CO,  represent? 

44  :  96  : :  0.001966  :  x.     x  =  0.004289  gm. 

Thus  each  cc.  of  COa  at  normal  pressure  and  o°  C. 
represents  0.004289  gm.  of  (NH4)aCO3,  approximately. 


A  TEXT-BOOK  OF   VOLUMETRIC  ANALYSIS.       353 


CHAPTER  XXXVII. 
ESTIMATION  OF  UREA  IN  URINE. 

THIS  determination  is  based  upon  the  fact  that  when 
urea  is  decomposed  by  an  alkaline  hypochlorite  or 
hypobromite,  carbon  dioxide  and  nitrogen  are  given 
off,  as  the  equation  shows: 

CO(NH3)3  +  3NaBrO  =  3NaBr  +  CO2  +  N2  +  2HaO. 

The  liberated  N  may  be  measured,  and  from  its  quan- 
tity the  quantity  of  urea  calculated  ;  the  other  products 
of  the  decomposition  go  into  solution. 

The  hypobromite  solution  is  prepared  as  follows  : 
100  gms.  NaOH  are  dissolved  in  250  cc.  of  water,  and 
when  this  solution  has  become  cold  25  cc.  of  bromine 
are  added,  and  the  solution  kept  cold.  This  solution 
contains  sodium  hypobromite,  bromate,  and  hydrox- 
ide ;  it  readily  undergoes  decomposition,  and  should 
therefore  always  be  freshly  prepared  when  wanted  for 
use. 

The  solution  of  sodium  hypochlorite  is  generally 
preferred  to  the  hypobromite,  because  it  is  more  stable, 
just  as  efficacious,  and  the  disagreeable  handling  of 
bromine  is  obviated. 

Various  forms  of  apparatus  have  been  devised  for 
the  quantitative  estimation  of  urea. 

The  simplest  of  these  is  probably  the  one  devised 
by  Dr.  Chas.  A.  Doremus.  (See  Fig.  35.) 


354      A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 


0 


The  long  arm  of  the  ureometer  is 
filled  with  the  hypobromite  solution, 
and  then  I  cc.  of  the  urine  is  intro- 
duced by  the  aid  of  the  pipette. 
The  pipette  is  introduced  through 
the  bulb  as  far  as  it  will  go  in  the 
bend,  and  the  nipple  is  then  gently 
but  steadily  compressed,  being  careful 
that  no  air  is  admitted. 

The  volume  of  the  liberated  gas  is 
read  off  after  the  froth  has .  sub- 
sided. 

The  ureometer  indicates,  according 
to  its  graduation,  either  milligrammes 
of  urea  in  I  cc.  or  grains  of  urea  per 
FIG.  35.  fluid  ounce  of  urine. 

It  also  indicates  by  the  signs  -J-,  N,  and  — 
whether  the  urea  is  present  in  an  increased, 
normal,  or  decreased  quantity. 

Another  Convenient  Form  of  Apparatus  is 
a  tube  closed  at  one  end,  and  graduated  so 
that  each  division  indicates  a  grain  of  urea  in 
a  fluid  ounce  of  urine,  when  I  cc.  of  urine  is 
taken  for  the  estimation.  (See  Fig.  36.) 

The  process  is  conducted  as  follows:  A  25- 
per-cent.  solution  of  KBr  is  introduced  to  the 
fifth  division.  The  chlorinated-soda  solution 
is  then  added  to  the  fifteenth  or  twentieth 
division.  The  tube  is  now  inclined,  and  pure 
water  carefully  poured  upon  the  liquid  so  that 
it  will  float  on  top;  i  cc.  of  urine  is  then  added 
carefully,  so  that  it  will  not  mix  with  the  re- 
agents below,  but  remain  in  the  water  at  the  FlG>  36- 
surface  of  the  fluid.  The  open  end  of  the  tube  is  then 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       355 

quickly  closed  with  the  thumb,  and  the  top  firmly 
grasped  in  the  right  hand.  The  tube  is  then  inverted, 
and  the  contents  well  mixed.  The  decomposition 
which  takes  place  is  usually  ended  in  five  minutes.  As 
soon  as  the  effervescence  has  ceased,  the  reading  is 
taken  at  the  surface  of  the  liquid.  The  tube  is  now 
opened  under  water,  when  the  column  of  fluid  in  the 
tube  will  fall;  the  reading  is  then  again  taken.  The 
difference  between  the  two  readings  gives  the  number 
of  grains  of  urea  in  a  fluid  ounce  of  the  urine. 

Squibb' s  Urea  Apparatus  (Fig.  37)  is  a  very  simple 
apparatus,  and  can  be  easily  improvised  in  a  drug-store. 
It  consists  of  two  wide-mouthed  bottles,  the  larger  of 
which  (C\  capable  of  holding  about  250  cc.,  is  fitted 
with  a  rubber  stopper,  through  which  is  passed  a  curved 


FIG.  37. 

delivery-tube  and  a  short  straight  tube,  the  latter  con- 
nected by  a  piece  of  rubber  tubing  to  the  short  glass 
tube  in  the  rubber  stopper  of  the  smaller  bottle  or 
generating-bottle  (B).  In  the  generating-bottle  is  a 
small  test-tube  (A). 

Into  the  test-tube  A  is  placed  5  cc.  of  urine,  and  into 
the  smaller  bottle  B  is  put  20  cc.  of  the  hypobromite 
solution,  or  strong  liquor  sodae  chlorinatae.  The  test- 
tube  is  then  placed  in  the  generating-bottle  B,  being 
careful  that  the  urine  and  the  reagent  do  not  come  in 
contact.  The  larger  bottle  C  is  now  filled  with  water 


356      A  TEXT-BOOK   OF   VOLUMETRIC  ANALYSIS. 

and  the  two  bottles  connected  by  the  rubber  tube,  the 
larger  bottle  being  placed  on  its  side  upon  a  block,  and 
when  all  connections  are  tight,  the  generating-bottle  is 
shaken  so  that  the  urine  will  mix  with  the  reagent. 

Decomposition  takes  place,  and  the  generated  gas 
passes  into  the  bottle  C,  displacing  water,  which  is 
caught  in  a  graduated  cylinder  or  other  measuring 
vessel.  The  volume  of  water  displaced  is  equivalent 
to  the  volume  of  gas  evolved. 

Each  cc.  of  nitrogen  gas  evolved  at  o°  C.  and  normal 
pressure  represents  0.0027  gm.  of  urea.  Then  by  mul- 
tiplying the  number  of  cc.  evolved  by  this  number  the 
quantity  of  urea  in  the  5  cc.  of  urine  taken  is  ascer- 
tained. 

The  volume  of  gas  obtained  when  the  operation  is 
conducted  at  ordinary  temperatures  should  always  be 
reduced  to  its  corresponding  volume  at  o°  C.  and  760 
mm. 

The  factor  0.0027  is  found  in  the  following  manner: 

1000  cc.  of  H  at  o°  C.  weigh  0.0896  gm. ; 
looo  cc.  of  N  at  o°  C.  weigh  1.2544  gms. 

By  the  equation  it  is  seen  that  60  gms.  of  urea 
evolve  when  decomposed  28  gms.  of  N. 

CO(NH2)2  +  3NaBrO  =  sNaBr  +  CO2  +  N2  +  2H2O. 

60  gms.  28  gms. 

Now  we  will  find  the  volume  occupied  by  28  gms.  of 
N  at  o°  C. 

1.2544  gms.  of  N  =  1000  cc. 

gms.          cc.         gms.  cc. 

1.2544  :  1000  :  :  28  :  x.     x  —  22321.43  cc. 

Thus  60  gms.  of  urea  evolve  22321.43  cc.  of  N  ;  I  cc. 
of  N  thus  represents  0.0027  gm.  of  urea. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       357 


CHAPTER   XXXVII.     . 
HYDROGEN    DIOXIDE 

As  stated  in  a  previous  chapter,  hydrogen  dioxide 
when  acted  upon  by  an  acidulated  solution  of  potas- 
sium permanganate,  is  decomposed  and  oxygen  is 
evolved.  One  half  of  this  oxygen  comes  from  the 
dioxide  and  the  other  half  from  the  permanganate. 

Therefore  if  I  cc.  of  the  dioxide  be  treated  in  this 
way  and  20  cc.  of  oxygen  are  evolved,  the  strength  of 
the  solution  is  10  volumes. 

The  nitrometer  may  be  used  for  this  estimation. 

This  instrument  is  charged  with  a  concentrated  solu- 
tion of  sodium  sulphate  (which  in  this  case  is  better 
than  brine),  and  I  cc.  of  the  dioxide  introduced  from 
the  funnel,  followed  by  excess  of  solution  of  perman- 
ganate acidulated  with  sulphuric  acid. 

This  latter  solution  should  be  of  such  strength  that 
when  the  reaction  is  completed,  the  solution  should 
still  have  a  purple  color. 

The  reaction  is  thus  illustrated: 

aOa  +  3H2S04  +  2KMn04 

=  KaSO4  +  2MnSO4  +  8H2O  +  $0,. 


By  the  use  of  Squibb 's  Urea  Apparatus  the  estima- 
ion  may  be  easily  and  rapidly  made. 
Into  the  generating-bottle  is  put  about  30  cc.  of  a 


358       A  TEXT-BOOK  OF  VOLUMETRIC   ANALYSIS. 

strong,  acidulated  solution  of  potassium  permanganate, 
and  a  small  test-tube  containing  I  cc.  of  H2O2  is  care- 
fully introduced.  The  two  liquids  must  not  be  allowed 
to  come  in  contact. 

The  larger  flask  is  filled  with  water  or,  better,  a  solu- 
tion of  sodium  sulphate,  the  connection  is  then  made 
by  means  of  the  rubber  tube,  and  the  generating-bottle 
tipped  over  and  agitated  so  that  the  liquids  will  mix 
and  the  reaction  take  place. 

The  liberated  oxygen  then  passes  into  the  larger 
bottle,  displacing  an  equal  volume  of  water,  which  is 
collected  and  measured.  Half  of  this  volume  repre- 
sents the  volume  strength  of  the  H2O,,. 

An  Improvised  Nitrometer  may  be  used.  The  au- 
thor has  found  the  following  instrument  convenient : 

To  the  bottom  of  an  ordinary  5O-cc.  burette  is  at- 
tached a  suitable  length  of  rubber  tubing,  to  the  other 
end  of  which  is  attached  another  burette  or  ungradu- 
ated  tube,  which  serves  as  a  control-tube. 

Into  the  top  of  the  burette  is  fitted  a  rubber  stopper, 
through  which  passes  a  short  glass  tube,  which  is  con- 
nected by  means  of  a  rubber  tube  to  a  generating-bot- 
tle similar  to  that  used  with  Squibb 's  Urea  Apparatus. 
Into  the  control-tube  is  poured  the  solution  of  so- 
dium sulphate,  -sufficient  to  fill  the  burette  to  the  zero- 
mark  and  have  the  surface  of  the  liquid  in  both  tubes 
on  a  level. 

About  30  cc.  of  strong  permanganate  solution  acidu- 
lated with  sulphuric  acid  are  now  placed  in  the  gener- 
ating-bottle, and  then  the  small  test-tube  or  homo- 
pathic  vial,  containing  exactly  I  cc.  of  hydrogen  diox- 
ide, is  placed  in.  The  generating-bottle  is  then  stop- 
pered and  agitated,  the  evolved  gas  passes  over,  and 


A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS.       359 

forces  the  liquid  in  the  burette,  down.  The  control- 
tube  is  then  lowered  so  as  to  bring  the  surfaces  of  the 
liquid  in  both  tubes  on  a  level. 

The  reading  is  then  taken. 

Each  cc.  of  gas  represents  £  volume  of  oxygen 
evolved  from  the  peroxide  if  I  cc.  of  the  latter  is  used. 
Each  cc.  of  oxygen  evolved  from  I  cc.  of  the  peroxide 
represents  also  0.001696  gm.  of  absolute  H2O2 ,  or 
0.0008  gm.  of  available  oxygen. 

Thus  if  from  I  cc.  of  the  solution  of  hydrogen  per- 
oxide, 20  cc.  of  gas  are  evolved,  it  is  a  so-called  10- 
volume  solution,  and  contains  .001696  X  20  =  0.03392 
gm.  of  absolute  HaO3,  or  0.0008  X  20  =  0.016  gm.  of 
available  oxygen. 


300      A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 


APPENDIX. 
INDICATORS. 

ACCORDING  to  R.  A.  Cripps,  the  requirements  of  a 
good  indicator  are  : 

I.  The  end  reaction  should  be  marked  by  a  promi- 
nent change  of  color. 

II.  The   smallest    possible   quantity  of  the  reagent 
should  be  required  to  effect  this  change. 

III.  High  tinctorial  power,  which  of  itself  assists  in 
the  fulfilment  of  the  second    requirement,  less  of  the 
indicator  being  required. 

IV.  The  change  of  color  should  not  be  effected  by 
the  impurities   commonly  present  in  the  substance  un- 
der examination,  nor  by  the  products  of  the  reaction. 

In  addition  to  these  requirements  it  is  a  distinct  ad- 
vantage if  the  color  reaction  is  equally  decided  in  al- 
coholic as  in  aqueous  liquids. 

Litmus. — The  coloring  principles  of  litmus  are  azolit- 
min,  erythrolitmin,  and  erythrolein.  The  first,  which  is 
the  most  important,  is  soluble  in  water,  but  insoluble 
in  alcohol.  The  other  two  are  readily  soluble  in  alcohol, 
but  only  sparingly  soluble  in  water. 

The  U.  S.  P.  process  for  making  litmus  test-solution, 
consists  in  exhausting  coarsely  powdered  litmus  with 
boiling  alcohol. 

The  residue  is  then  digested  with  about  an  equal 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.       361 

weight  of  cold  water  so  as  to  dissolve  the  excess  of 
alkali  present. 

The  blue  solution  thus  obtained,  after  being  acidu- 
lated may  be  used  to  make  red  litmus-paper.  Finally, 
the  residue  is  extracted  with  about  five  times  its  weight 
of  boiling  water,  and  the  solution  filtered. 

The  filtrate  is  preserved  as  test  solution,  in  wide- 
mouthed  bottles,  stoppered  with  loose  plugs  of  cotton 
to  exclude  dust,  but  to  admit  air. 

When  kept  in  closed  vessels  litmus  solution  gradu- 
ally loses  color,  but  this  returns  upon  exposure  to  air 
and  consequent  absorption  of  oxygen. 

The  fermentation  to  which  the  loss  of  color  is  due 
may  be  prevented  by  saturating  the  solution  with 
NaCl. 

The  British  Pharmacopoeia  recommends  to  boil  the 
litmus  in  powder  with  three  successive  portions  of  rec- 
tified spirit,  and  then  to  digest  the  residue  in  distilled 
water,  and  filter,  the  object  of  these  steps  in  the  pro- 
cess being  to  get  rid  of  the  greater  portion  of  ery- 
throlitmin  and  erythrolein,  which  are  soluble  in  alcohol. 
Then  by  treating  the  residue  with  water  a  larger  pro- 
portion of  azolitmin  is  dissolved,  and  the  solution  is  con- 
taminated with  very  little  of  the  other  two  principles. 

Litmus  may  be  used  in  a  very  large  number  of  titra- 
tions.  It  is  of  value  in  the  titration  of  most  mineral 
acids  and  of  a  few  organic  acids,  e.  g.,  benzoic  and  oxalic. 
It  is  also  useful  in  the  titration  of  alkaline  hydroxides 
when  the  latter  are  free  from  carbonates. 

But  for  carbonates,  bicarbonates,  etc.,  a  reliable 
end  reaction  can  only  be  obtained  by  boiling  the 
solution  during  the  titration,  in  order  to  dispel  the 
liberated  COa. 


362       A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS. 

Free  CO,  has  an  acid  reaction  with  litmus,  and  inter- 
feres very  much  with  the  rinding  of  the  end  reaction. 

Litmus  may  be  used  for  ammonia  and  for  borax. 
It  is  of  no  use  for  phosphoric  or  arsenic  acid,  nor  for 
phosphates  or  arsenates,  because  the  change  of  tint  is 
too  gradual. 

It  is  unsatisfactory  in  titrating  many  organic  acids, 
e.g.,  tartaric  arid  citric. 

Sometimes  it  is  required  to  perform  a  titration  with 
litmus  at  night.  Gas  or  lamp  light  is  not  adapted  for 
showing  the  reaction  satisfactorily,  but  by  using  a 
monochromatic  light,  such  as  the  sodium  flame,  a  very 
sharp  line  of  demarcation  may  be  found. 

The  operation  should  be  conducted  in  a  dark  room  ; 
using  a  piece  of  platinum-foil  sprinkled  with  salt  or  a 
piece  of  pumice-stone  saturated  with  a  solution  of  salt, 
heated  in  a  Bunsen  flame. 

The  red  color  then  appears  perfectly  colorless,  while 
the  blue  appears  like  a  mixture  of  ink  and  water. 

Phenolphthalein. — Preparation. — 5  parts  of  phthalic 
anhydride  (C8H4O3),  JO  parts  of  phenol  (C9HBOH), 
and  4  parts  of  H2SO4  are  heated  together  at  120°  to 
130°  C.  for  several  hours.  The  product  is  then  boiled 
with  water,  and  the  residue,  which  consists  of  impure 
phenolphthalein,  is  dissolved  in  dilute  soda  solution 
and  filtered.  By  neutralizing  this  solution  the  phenol- 
phthalein is  precipitated,  and  may  be  purified  by  crys- 
tallization from  alcohol ;  or  the  alcoholic  solution  may 
be  boiled  with  animal  charcoal,  filtered,  and  the 
phenolphthalein  reprecipitated  by  boiling  water. 

Uses. — Phenolphthalein  is  a  very  valuable  indicator; 
it  is  extremely  sensitive,  and  exhibits  a  well-marked 
and  prompt  change  from  colorless  to  pink,  and  vice  versa. 


A  TEXT-BOOK  OF  VOLUMETRIC  ANALYSIS.      363 

A  few  drops  of  the  solution  of  the  indicator  show  no 
color  in  neutral  or  acid  liquids,  but  the  faintest  excess 
of  alkali  produces  a  sudden  change  to  red. 

It  may  be  employed  in  the  titration  of  mineral  and 
organic  acids  and  most  alkalies,  but  it  is  not  suited 
for  the  titration  of  ammonia  or  its  salts.  It  is  very 
sensitive  to  CO3,  and  therefore  in  estimating  carbon- 
ates the  liquid  must  be  boiled,  as  with  litmus.  It  is 
inapplicable  for  borax,  because  the  color  gradually 
fades  away  as  the  acid  is  added.  One  great  advantage 
which  phenolphthalein  possesses  is  that  its  indications 
may  be  clearly  read  in  many  colored  liquids ;  another 
is  that  it  may  be  used  in  alcoholic  liquids  or  in  mix- 
tures of  alcohol  and  ether,  and  therefore  many  organic 
acids  which  are  insoluble  in  water  may  be  accurately 
titrated  by  its  help. 

Phenolphthalein  T.  S.  is  prepared  as  follows  :  Dis- 
solve I  gm.  of  phenolphthalein  (C20H14O4)  in  100  cc. 
of  diluted  alcohol  U.  S.  P. 

Methyl-orange. — Porrier's  Orange  III,  Tropaeolin 
D,  Helianthin,  Mandarin-orange,  para-sulpho-benzene- 
azo-dimethylaniline. 

This  is  prepared  by  the  action  of  diazo-sulphanilic 
acid  upon  dimethylaniline ;  the  acid  so  formed  is  con- 
verted into  a  sodium  or  ammonium  salt,  purified  by 
reprecipitation  with  HC1,  and  again  converted  into  a 
sodium  or  ammonium  salt.  If  prepared  carefully  and 
from  the  purest  materials,  it  is  a  bright  orange-red 
powder,  perfectly  soluble  in  water  and  slightly  soluble 
in  alcohol ;  but  it  is  often  found  in  commerce  as  a  dull 
orange-brown  powder,  often  not  completely  soluble  in 
water.  Many  conflicting  statements  have  been  made 
by  operators  as  to  the  value  of  methyl-orange  as  an 


364      A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS. 

indicator,  which  have  tended  to  bring  this  indicator 
into  disrepute. 

Sutton  has  examined  many  specimens,  but  has  not 
found  any  in  which  the  impurities  sensibly  affected  its 
delicate  action.  He  claims  that  the  common  error  is 
the  use  of  too  much  indicator,  and  that  some  eyes  are 
more  sensitive  to  a  change  of  tint  than  o.thers. 

Methyl-orange  is  no  doubt  a  very  good  indicator, 
but  practice  with  it  must  be  had,  in  order  to  obtain 
good  results.  The  author  has  found  one  sample  which 
had  a  beautiful  orange  color,  but  which  was  absolutely 
useless  as  an  indicator. 

A.  H.  Allen  describes  as  follows  the  characters  and 
tests  of  a  good  article  : 

1.  Aqueous    solution,   not   precipitated   by  alkalies. 
(Orange  I  becomes    red-brown;    orange    II   brownish 
red.) 

2.  Hot  concentrated   aqueous  solution  yields  with 
HC1  microscopic  acicular  crystals  of  the  free  sulphonic 
acid,  soon  changing  to  small  lustrous  plates  or  prisms 
having  a  violet   reflection.     (Orange   I   gives   yellow- 
brown    color    or    flocculent    precipitate ;     orange    II 
brown-yellow  precipitate.) 

3.  Dissolves  in  concentrated   H2SO4  with  a  reddish 
or  yellowish-brown  color,  which  on  dilution  becomes 
fine  red. 

4.  BaCl2  yields  a  precipitate. 

5.  CaCl2  yields   no  precipitate.     Orange   I  gives  a 
red  precipitate.) 

6.  Pb(C2H3O2)3  yields  an  orange-yellow  precipitate. 

7.  MgSO4  in  dilute  solutions  precipitates  the  color- 
ing matter  in  microscopic  crystals. 

Methyl-orange  T.  S.  is  made  by  dissolving  i  gm. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       365 

of  methyl-orange  in  IOOO  cc.  of  water.  Add  to  it  care- 
fully diluted  sulphuric  acid  in  drops,  until  the  liquid 
turns  red  and  just  ceases  to  be  transparent.  Then 
filter. 

The  great  value  of  this  indicator  consists  in  the  fact 
that  it  is  not  affected  by  carbonic-acid  gas,  sulphuretted 
hydrogen,  or  boric,  silicic,  arsenous,  oleic,  stearic,  and 
many  other  acids. 

It  answers  well  for  ammonia,  but  it  is  useless  for 
most  of  the  organic  acids.  Phosphoric  and  arsenic 
acids  are  rendered  neutral  to  methyl-orange  when  only 
one  third  of  the  acid  has  combined  with  the  base,  the 
end  reaction  being  well  defined.  (Phenolphthalein  in- 
dicates neutrality  when  two  thirds  of  acid  are  combined.) 

Rosolic  Acid,  C20HUO3. — This  compound  is  also 
called  Aurin  and  Corallin,  and  is  prepared  as  follows : 

A  mixture  of  phenol  and  sulphuric  acid  is  placed 
upon  a  water-bath,  and  oxalic  acid  gradually  added, 
waiting  each  time  till  the  evolution  of  gas  ceases,  and 
using  less  oxalic  acid  than  is  required  to  attack  all  the 
phenol. 

In  this  process  the  oxalic  acid  is  decomposed  into 
CO,  CO,,  and  HaO.  The  CO  immediately  reacts  with 
the  phenol  and  forms  rosolic  acid,  as  the  following 
equation  shows : 

3C,H6OH  +  2CO  =  C,0H1403  +  2H,0. 

Rosolic  acid  is  soluble  in  50$  alcohol.  Its  color  is 
pale  yellow,  unaffected  by  acids,  but  turning  violet-red 
with  alkalies. 

It  is  an  excellent  indicator  for  all  the  mineral  acids, 
but  is  not  reliable  for  the  organic  acids,  excepting 
oxalic. 


366       A  TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS. 

Rosolic-acid  Test  Solution,  U.  S.  P. — Dissolve  i 
gm.  of  commercial  rosolic  acid  (chiefly  methylaurin, 
Ca(,H16O3)  in  10  cc.  of  diluted  alcohol,  and  add  enough 
water  to  make  100  cc.  The  solution  turns  violet-red 
with  alkalies,  yellow  with  acids.  In  place  of  rosolic 
acid,  commercial  paeonin  (also  known  as  aurin  R) 
[chiefly  C19H14O3]  may  be  employed. 

Fluorescein  or  Resorcin  Phthalein  C2nH12O5,  is  pre- 
pared by  heating  resorcin  with  phthalic  anhydride 
to  200°  C.  Dark-brown  crystals  are  formed,  which 
dissolve  in  ammonia,  forming  a  red  solution,  with  a 
splendid  green  fluorescence. 

Fluorescein  Test  Solution,  U.  S.  P. — Agitate  i  gm. 
of  fluorescein  with  100  cc.  of  diluted  alcohol  until  the 
latter  is  saturated  ;  then  filter. 

Eosin,  or  Tetra-bromo-resorcin-phthalein. — This  is 
made  by  adding  bromine  to  a  solution  of  fluorescein 
in  glacial  acetic  acid.  Crystals  gradually  separate, 
which  may  be  purified  by  conversion  into  a  potassium 
salt  and  precipitated  with  an  acid. 

The  composition  of  this  substance  is  K2C29H6Br4O3. 

Eosin  Test  Solution,  U.  S.  P. — Dissolve  i  gm.  of 
commercial  yellowish  eosin  in  30  cc.  of  water. 

Corallin  Test  Solution,  U.  S.  P.— Dissolve  i  gm.  of 
corallin  (a  coloring  matter  derived  from  coal-tar,  and 
containing  rosolic  and  para-rosolic  acids)  in  10  cc.  of 
alcohol  and  enough  water  to  make  100  cc. 

Gallein. — Anthracene  violet  or  pyrogallo-phthalein 
was  proposed  by  M.  Dechan  for  use  as  an  indicator. 

It  is  prepared  by  heating  a  mixture  of  one  part  of 
phthalic  anhydride  and  two  parts  of  pyrogallol,  and 
finally  recrystallizing  in  a  similar  way  to  phenolphtha- 
lein. 


A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.       367 

It  is  described  as  a  dark  reddish  crystalline  solid, 
possessing  a  greenish  lustre.  It  is  nearly  insoluble  in 
water,  but  readily  soluble  in  alcohol.  In  commerce  it 
is  frequently  found  as  a  paste,  mixed  with  water. 

It  forms  a  violet-pink  coloration  with  alkalies,  which 
is  changed  to  yellowish  brown  on  addition  of  an  acid 
in  excess. 

It  is  said  to  be  more  delicate  towards  alkalies  than 
phenolphthalein,  and  may  be  used  in  its  stead  for 
titrating  many  of  the  alkaloids.  It  may  be  used  in  the 
presence  of  ammonia  or  its  salts.  It  indicates  sharply 
with  the  organic  acids.  A  solution  in  rectified  spirit 
i-iooo  is  generally  employed. 

Lacmoid  is  somewhat  allied  to  litmus,  but  differs 
from  it  in  many  respects.  It  is  a  product  of  resorcin, 
and  may  be  prepared  by  heating  gradually  to  110°  C. 
a  mixture  of  100  parts  of  resorcin,  5  parts  of  sodium 
nitrite,  and  5  parts  of  water.  After  the  violent  reac- 
tion moderates  it  is  heated  to  120°  C.  until  ammonia 
ceases  to  be  evolved.  The  residue  is  then  dissolved  in 
warm  water  and  the  lacmoid  precipitated  therefrom 
by  HC1 ;  the  free  acid  is  then  removed  by  washing 
and  the  residue  dried. 

Lacmoid  is  soluble  in  dilute  alcohol.  A  solution 
containing  2  gms.  in  a  litre  is  generally  employed. 

Lacmoid  Paper. — This  is  prepared  by  dipping  slips 
of  calendered  unsized  paper  into  the  blue  or  red  solu- 
tion and  drying  them. 

Lacmoid  is  affected  by  carbonic-acid  gas.  It  may 
be  used  cold  for  the  alkaline  and  earthy  hydroxides, 
arsenites,  and  borates,  and  the  mineral  acids.  The 
carbonates  and  bicarbonates  of  the  alkalies  and  alka- 
line earths  are  titrated  hot  with  this  indicator. 


368       A   TEXT-BOOK   OF   VOLUMETRIC   ANALYSIS 

Many  of  the  metallic  salts,  such  as  the  sulpnates 
and  chlorides  of  iron,  copper,  and  zinc,  which  are  more 
or  less  acid  to  litmus,  are  neutral  to  lacmoid;  therefore 
free  acids  in  such  solutions  may  be  estimated  by  its 
aid. 

Lacmoid  paper  reacts  alkaline  with  the  chromates  of 
potassium  or  sodium,  but  neutral  with  the  dichromates, 
so  that  a  mixture  of  the  two  or  of  chromic  acid  and 
dichromate  may  be  titrated  by  its  aid. 

Phenacetolin. — This  may  be  prepared  by  boiling 
together  for  several  hours  equal  molecular  proportions 
of  phenol,  acetic  anhydride,  and  sulphuric  acid.  The 
product  is  then  well  washed  with  water  to  remove  ex- 
cess of  acid,  and  dried  for  use.  It  is  soluble  only  in 
alcohol,  and  a  convenient  strength  of  solution  is  2  gms. 
per  litre.  The  solution  is  dark  brown,  which  gives  a 
scarcely  perceptible  yellow  with  caustic  soda  or  po- 
tassa,  when  a  few  drops  are  used  with  the  ordinary  vol- 
umes of  liquid.  With  the  normal  alkaline  carbonates 
and  with  ammonia  it  gives  a  dark  pink,  with  bicarbo- 
nate a  much  more  intense  pink,  and  with  the  mineral 
acids  a  golden  yellow. 

This  indicator  may  be  used  for  estimating  the 
amount  of  caustic  potash  or  soda  in  the  presence  of 
their  normal  carbonates.  Practice  is,  however,  re- 
quired, so  as  to  acquire  knowledge  of  the  exact  shades 
of  color. 

Cochineal  Test  Solution,  U.  S.  P.— Macerate  i 
gm.  of  unbroken  cochineal  during  four  days  with  20 
cc.  of  alcohol  and  60  cc.  of  water,  then  filter.  The 
color  of  this  test  solution  turns  violet  with  alkalies  and 
yellowish  red  with  acids. 

Brazil-wood  Test  Solution,  U.  S.  P.— Boil  50  gms. 


A  TEXT- BOOK   OF   VOLUMETRIC   ANALYSIS.       369 

of  finely  cut  Brazil-wood  [the  heart-wood  of  Pelto- 
phorum  dubium  (Sprengel)  Britton,  nat.  ord.  Legumi- 
nosce}  with  250  cc.  of  water  during  half  an  hour,  re- 
placing from  time  to  time.  Allow  the  mixture  to 
cool ;  strain  ;  wash  the  contents  of  the  strainer  with 
water  until  100  cc.  of  strained  liquid  are  obtained : 
add  25  cc.  of  alcohol  and  filter.  This  solution  turns 
purplish  red  with  alkalies  and  yellow  with  acids. 

Turmeric  Tincture,  U.  S.  P. — Digest  any  conven- 
ient quantity  of  ground  curcuma-root  [from  Curcuma 
longa  Linne,  nat.  ord.  Scitaminece}  repeatedly  with 
small  quantities  of  water,  and  throw  this  liquid  away. 
Then  digest  the  dried  residue  for  several  days  with  six 
times  its  weight  of  alcohol,  and  filter. 

Turmeric  Paper. — Impregnate  white,  unsized  paper 
with  the  tincture  and  dry  it. 

REAGENTS  AND   TEST   SOLUTIONS. 

Ammonium-carbonate  Test  Solution. — 10  gms.  of 
ammonium  carbonate  NH4HCO3.NH4NH2CO2  are  dis- 
solved in  a  mixture  of  10  cc.  of  ammonia-water  and  40 
cc.  of  water. 

Ammonium-chloride  Test  Solution. — 10  gms.  of 
NH4C1  are  dissolved  in  sufficient  water  to  make  100  cc. 

Ammonium-molybdate  Test  Solution. — i  gm.  of 
finely  powdered  ammonium  molybdate  (NH4)2MoO4  is 
dissolved  in  6.7  cc.  of  hot  water,  using  a  little  am- 
monia-water, if  necessary,  to  effect  solution  ;  the  liquid 
is  then  poured  gradually  into  a  mixture  of  3.3  cc.  of 
nitric  acid  (sp.  gr.  1.414)  and  3.4  cc.  of  water. 

The  solution  should  be  preserved  in  the  dark,  and  if 
a  sediment  should  form  in  it  after  some  days,  carefully 
decant  the  clear  solution  from  it. 


370       A  TEXT-BOOK   OF  VOLUMETRIC  ANALYSIS.      • 

Ammonium-oxalate  Test  Solution. — i  gm.  of 
pure  crystallized  ammonium  oxalate  in  sufficient  water 
to  make  100  cc. 

Barium-chloride  T.  S. — 12.2  gms.  of  the  pure 
salt  in  enough  water  to  make  100  cc. 

Cupric-sulphate  T.  S.— 10  gms.  of  CuSO4  +  5H2O 
in  water  to  make  100  cc. 

Ferric-ammonium  Sulphate  T.  S. — 10  gms.  of 
ferric  ammonium  sulphate  in  water  to  make  100  cc. 

Hydrochloric  Acid,  Pure,  for  Tests,  HCL  See 
U.  S.  P. 

Indigo  T.  S. — Place  6  gms.  of  fuming  sulphuric 
acid  into  a  beaker  well  cooled  by  immersion  in  water, 
and  stir  into  it  very  gradually  I  gm.  of  finely  powdered 
Bengal  indigo.  Set  the  mixture  aside  for  two  days, 
then  pour  it  into  20  cc.  of  water,  and  decant.  Or,  dis- 
solve i  gm.  of  commercial  indigo-carmine  (the  sodium 
or  potassium  salt  of  sulphindigotic  acid)  in  150  cc.  of 
water. 

Iodine  T.  S. — Iodine  i  gm.,  potassium  iodide  3  gms., 
water  50  cc. 

Iron  (Metallic)  Fe.— See  U.  S.  P. 

Magnesium  Sulphate  T.  S. — 10  gms.  of  MgSO4+ 
7H2O  in  water  to  make  100  cc. 

Nitric  Acid,  Pure,  for  Tests,  HNO3.— See  U.  S.  P. 

Potassium  Chromate  T.  S. — Dissolve  i  gm.  of 
K,CrO4  in  enough  water  to  make  10  cc.  On  adding 
silver  nitrate  T.  S.  to  a  little  of  the  solution  a  red  pre- 
cipitate is  produced,  which  should  be  completely  dis- 
solved by  nitric  acid  (absence  of  chloride).  Another 
portion  of  the  solution  mixed  with  an  equal  volume  of 
diluted  hydrochloric  acid  should  yield  no  precipitate 
with  barium  chloride  T.  S.  (absence  of  sulphate). 


A  TEXT-BOOK   OF  VOLUMETRIC   ANALYSIS.       371 

Potassium  Ferricyanide  T.  S. —  i  part  of  K6Fe 
(CN)ia  in  about  10  parts  of  water.  Should  be  freshly 
prepared  when  wanted. 

Potassium  Hydroxide  T.  S.— Use  the  official 
liquor  potassae. 

Potassium  Iodide  T.  S. — 16.556  gms.  of  KI  in 
enough  water  to  make  100  cc.  The  solution  should  be 
kept  in  dark-amber  colored,  well-stoppered  bottles  to 
prevent  the  formation  of  iodate.  It  is  well  to  renew  it 
frequently  or  prepare  it  freshly  when  wanted. 

Silver  Nitrate  T.  S. — For  ordinary  purposes  use 
the  decinormal  volumetric  solution. 

Sodium  Hydroxide  T.  S. — Use  the  official  liquor 
sodae. 

Starch  T.  S.  — Mix  i  gm.  of  starch  with  10  cc.  of 
cold  water,  and  then  add  enough  boiling  water,  under 
constant  stirring,  to  make  200  cc.  of  a  thin,  transparent 
jelly. 

Sulphuric  Acid,  Pure,  for  Tests,  HaSO4  .—See  U. 
S.  P. 

For  other  test  solutions  see  the  United  States  Phar- 
macopaeia. 


INDEX. 


PAGE 

Abbreviations xviii 

Acetate  of  iron,  solution  of 196 

potassium 61 

sodium 62 

Acetic  acid 73 

diluted 74 

glacial 76 

table 75 

Acid,  acetic 73 

diluted 74 

glacial 76 

table 75 

arsenous 163 

solution  of 164 

carbolic 268 

crude,  valuation  of 273 

estimation  of,  by  Waller's  method 272 

citric 76 

hydriodic,  syrup  of in 

hydrobromic,  diluted 77 

hydrochloric 78 

diluted 79 

standard  solutions  of 40 

hydrocyanic,  diluted 117 

hypophosphorous,  diluted 79,  146 

lactic 30 

muriatic 78 

nitric , . . .  81 

diluted 82 

oleic 246 

373 


374  INDEX. 

PAGE 

Acid,  oxalic 158 

standard  solutions  of •. 39 

phenyl-sulphate  solution 211 

phosphoric 82 

estimation  of,  by  Stolba's  method 84 

as  ammonio-magnesian  phosphate 84 

picric,  test  for  sugar 334 

rosolic 365 

T.  S 366 

sulphuric 86 

aromatic 87 

diluted 87 

standard  solutions  of 41 

sulphurous 165 

tannic 242 

tartaric 87 

uric 329 

arsenosi,  liquor 164 

Acidified  salt  solution , 244 

Acidimetry 36-68 

Acids,  estimation  of,  by  neutralization 68 

mineral,  in  vinegar 75 

Acidulated  brine  test  for  albumen 332 

Air,  carbonic  acid  in 223 

Albumen  in  urine 330 

acidulated  brine  test  for 332 

boiling  test  for 330 

ferrocyanide  test  for 331 

nitric-acid  test  for 331 

picric-acid  test  for 331 

potassio-mercuric-iodide  test  for 332 

quantitative  estimation  of 332 

sodium-tungstate  test  for 332 

Albuminoid  ammonia 210 

Albuminometer,  Esbach's , 332 

Alcohol  table 240 

Alcoholic  strength  of  beverages 238 

Alkalimetry 36-38 

Alkaline  carbonates 47 

earths..                                                             ......  88 


INDEX.  375 


Alkaline  hydroxides 43 

potassium-permanganate  solution 208 

Alkaloidal  assay  by  immiscible  solvents 292 

of  extracts,  general  method 295 

scale  salts 295 

Alkaloids,  volumetric  estimation  of 285 

by  Mayer's  reagent 290 

Alum,  ammonio-ferric 192 

Ammonia 46 

albuminoid , 210 

free  water 208 

in  water 207 

spirit  of 47 

stronger  water  of 47 

water  of 46 

Ammonio-ferric  alum 192 

sulphate 192 

tartrate 188 

Ammonium  bromide 99 

carbonate 47 

"       T.  S.  of 369 

chloride 109 

in  NH4Br 100 

solution  of,  for  water  analysis 208 

hydroxide , 46 

molybdate,  T.  S.  of 369 

Analyses,  gasometric . 342 

Analysis  by  indirect  oxidation 161 

neutralization. 36 

oxidation  with  potassium  dichromate 127,  136 

"  "  permanganate 141 

precipitation 96 

reduction ...   172 

saturation 36 

gravimetric I 

quantitative I 

volumetric 2 

of  soap 248 

urinary  calculi 340 

water 207 


376  INDEX. 

PAGE 

Antimony  and  potassium  tartrate 169 

Apparatus  used  in  volumetric  analysis 17 

Squibb's  urea , 355 

use  of 27 

Aqua  ammonia 46 

fortior 47 

chlori 177 

hydrogenii  dioxidi 152-154,  357 

Argenti  nitras. 121 

dilutus 123 

f  usus 123 

oxidum 123 

Arsenous  acid 163 

decinormal  V.  S.  of 181 

anhydride 163 

Arsenic  trioxide , 163 

Assay,  alkaloidal,  by  immiscible  solvents 292 

'    of  amyl  nitrite 347 

cinchona 302 

ethyl  nitrite 346 

extracts,  general  method  for  the 295 

extract  of  nux  vomica 296 

opium 298 

hydrogen  dioxide 152-154,  200,  357 

ipecac  root 306 

fl.  extr.  of 304 

nux  vomica,  extract  of 296 

fl.  extr.  of 298 

tincture  of 298 

opium 301 

extract  of 298 

tincture  of 300 

sodium  nitrite   350 

spirit  of  nitrous  ether 346 

Atmosphere,  carbonic  acid  in 223 

Back  titration 9 

Barium  chloride. 93 

dioxide 157 

hydroxide  solution,  standard , 233,  255 


INDEX.  377 


Barium  nitrate 93 

peroxide..., 157 

Baryta- water,  standard 233,   255 

Beale's  filter 291 

Benzoate  of  lithium 63 

sodium 64 

Beverages,  estimation  of  alcohol  in 238 

Bicarbonate  of  potassium 49 

sodium 50 

Bichromate  of  potassium  V.  S 129 

Bile  in  urine,  Gmelin's  test  for 338 

Oliver's  test  for 338 

Pettenkofer's  test  for 338 

tincture-of-iodine  test  for ........   339 

Ultzmann's  test  for 339 

Bink's  burette ... 19 

Bismuth  test  for  sugar  in  urine *  334 

Bisulphite  of  sodium 169 

Bitartrate  of  potassium 58 

Bleaching-powder 178 

arsenous-acid  process  for 180 

Blood  in  urine .. 333 

Borax 54 

Boyle's  law 344 

Brazil-wood  test  solution n,  368 

Bromide  of  ammonium 99 

calcium 92-103 

iron,  syrup  of 117 

lithium 101 

potassium 101 

sodium = 102 

strontium 103 

zinc , 104 

Bromine,  decinormal  solution  of 262 

Burette,  the 17 

Bink's 19 

clamp 25 

connected  with  reservoir 24 

Gay-Lussac's , 19 

glass  stop-cock 17 


37**  INDEX. 


PAGE 

Burette  holder 26 

how  cleaned 27 

how  filled 27 

Mohr's 25 

oblique  stop-cock 18 

with  bead  stop 20 

Butter,  composition  of 319 

Reichert's  piocess  for  the  detection  of  foreign  fats  in 319 

Calcium  bromide 91 

carbonate 91 

chloride ...» 93 

solution  221 

hydroxide 90 

hy  pophosphite 148 

Calculating  results 31 

Calx  chlorata 178 

Caustic  lime 90 

lunar , 123 

mitigated 1 23 

Carbolic  acid 268 

estimation  of,  by  Waller's  method 272 

crude,  valuation  of 273 

Carbonate  of  ammonium 47 

calcium 91 

iron,  saccharated 138 

lithium 51 

potassium 48 

sodium 49 

exsiccated 50 

Carbonates,  estimation  of 47 

by  the  nitrometer 352 

Carbonic-acid  gas,  estimation  of,  in  the  atmosphere 223 

table  showing  volume  of  .001  gm.  at  various 

temperatures 237 

Card,  half-blackened,  for  assistance  in  reading  graduated  instru- 
ments   29 

Centimeter,  cubic,  the 15 

Centinormal  solutions , 8 

potassium  hydroxide  V.  S 71 


INDEX.  379 

PAGE 

Centinormal  potassium  permanganate  V.  S 131 

Charles'  law 344 

Chloride  of  ammonium 109 

barium , 93 

calcium 93 

iron 184 

solution  of 185 

tincture  of 186 

lime , 178 

potassium 109 

sodium , no 

purification  of 122 

decinormal  V.  S.  of 122 

zinc no 

Chlorides  in  urine 326 

water 206 

Chlorinated  lime 178 

by  arsenous-acid  solution 180 

soda  solution.    178 

Chlorine,  available,  in  chlorinated  lime .. .  178 

by  arsenous-acid  solution 180 

soda  solution 181 

Chlorine  in  water 206 

water 177 

Chromate-of-potassium  solution 206 

Cinchona  assay 302 

Citrate  of  iron  ....   186 

solution 188 

and  ammonium 188 

quinine 189 

soluble 191 

strychnine   191 

lithium 59 

potassium 60 

Citric  acid 76 

Clamp,  for  burette 20 

Cochineal  test  solution 1 1,  368 

Coefficients  for  calculating  the  results  of  analyses 33 

Colostrum   310 

Copper-zinc  process  for  nitrates 214 


380  INDEX. 

PAGE 

Corallin  test  solution 368 

Cream  of  tartar 58 

Crude  carbolic  acid,  valuation  of » 273 

Cubic  centimetre,  the 15 

Cupric  tartrate,  alkaline  V.  S 259 

Cyanide  of  potassium 120 

Cyanides,  estimation  of,  by  iodine 120 

Dichromate  of  potassium  V.  S 129 

Decinormal  solutions 8 

arsenous  acid  V.  S 1 8 1 

bromine  V.  S 202 

hydrochloric  acid  V.  S 40 

iodine  V.  S 162 

Mayer's  solution 292 

mercuric  potassium  iodide  V.  S 292 

oxalic  acid  V.  S . . .    40 

potassium  dichromate  V.  S 129 

permanganate  V.  S 131 

sulphocyanate  V.  S 113 

salt  solution   122 

silver  nitrate  V.  S 97 

sodium  chloride  V.  S 122 

hyposulphite  V.  S 173 

tbiosulphate  V.  S 173 

sulphuric  acid  V.  S 41 

Diastasic  value  of  malt  extract 281 

Digitalin 308 

Digitaliretin 308 

Dioxide  of  barium 157 

hydrogen , 152-154,  200,  357 

Doremus'  ureometer 335 

Double-normal  solutions 8 

Empirical  solutions. 9 

Eosin ...    366 

test  solution n,  366 

Erdman's  float 29 

Estimation  of  acids,  by  neutralization  . .  68 

mineral,  in  vinegar 75 


INDEX.  381 

PAGE 

Estimation  of  alcohol  in  tinctures  and  beverages 238 

alkaline  carbonates 47 

earths 88 

hydroxides 43 

alkaloidal  strength  of  scale  salts 295 

alkaloids 285 

by  Mayer's  reagent *. 290 

carbonates  by  the  nitrometer 352 

carbonic  acid,  in  the  atmosphere 233 

fat  in  milk 314 

ointments , 252 

free  mineral  acids  in  vinegar 75 

ferric  salts 183 

ferrous  salts 128,  136,  141 

by  dichromate 136 

permanganate 141 

glucosides 308 

glycerine 262 

haloid  salts , 97 

hypophosphites 146 

hypophosphorous  acid  146 

iron  in  citrate  of  iron  and  quinine 190 

strychnine 191 

nitric  acid,  in  nitrates 350 

oil  in  emulsions 252 

oleic  acid ...  246 

organic  salts  of  the  alkaline  metals 54 

phenol 266 

by  Waller's  method 272 

quinine,  in  citrate  of  iron  and  quinine 189 

resin,  in  drugs 306 

salts  of  the  alkaline  earths 88 

halogens 97 

starch 255-258 

strength  of  resinous  drugs 306 

strychnine,  in  citrate  of  iron  and  strychnine 191 

substances,  readily  reduced 1 72 

sugar 259 

tannin,  Fleury's  method 242 

Lowenthal's  method. 243 


382  INDEX. 

PAGE 

Estimation  of  urea 353 

by  Doremus'  ureometer 353 

gas  tube 354 

Squibb's  urea  apparatus 355 

Estimations,  gasometric 342 

Ethyl  nitrite 346 

Examination,  chemical,  of  urinary  deposits 339 

microscopical,  of  urinary  deposits 339 

Factors  for  calculation  of  analyses 33 

Fat,  estimation  of,  in  milk 314 

Fats,  determination  of  melting-points 251 

estimation  of,  in  ointments 252 

Fehling's  solution 259 

estimation  of  sugar  by 259 

glucosides  by 308 

starch  by 258 

Fermentation  test  for  sugar  in  urine.  . 336 

Einhorn's 336 

Ferri  citratis,  liquor 187 

carbonas  saccharatus 138 

chloridum 184 

chloridi,  liquor 185 

tinctura 186 

citras 1 86 

liquor , « .  „ 187 

et  ammonii  citras 1 88 

sulphas 192 

tartras 1 88 

potassii  tartras 188 

quininae  citras 189 

solubilis 191 

strychninse  citras 19 r 

bromidi,  syrupus ....   117 

hypophosphis 149 

iodidum,  saccharatum 116 

iodidi,  syrupus 112^114 

nitratis,  liquor 197 

phosphas,  solubilis 188 

pyrophosphas  solubilis , 194 


INDEX.  383 

PAGE 

Ferri  sulphas 140 

exsiccatus 141-145 

granulatus 141-145 

subsulphatis,  liquor. . 198 

tersulphatis,  liquor 199 

valerianas 195 

Ferric  acetate  solution 196 

ammonium  citrate 188 

sulphate  192 

tartrate 188 

potassium  tartrate 188 

quinine  citrate ,   189 

soluble 191 

strychnine  citrate 191 

chloride 184 

solution 185 

tincture 186 

citrate 186 

solution  of 187 

hypophosphite 148 

nitrate  solution 197 

phosphate,  soluble 188 

pyrophosphate,  soluble 194 

salts,  estimation  of 183 

subsulphate  solution 198 

tersulphate  solution  199 

valerianate. 195 

Ferrous  bromide,  syrup  of 117 

carbonate,  saccharated 138 

iodide,  saccharated 116 

syrup  of 112-117 

salts,  estimation 128,  136,  141 

with  dichromate 136 

permanganate 141 

sulphate ....   140-145 

anhydrous 141 

dried 141-145 

exsiccated 141-145 

granulated ; 141-145 

Ferrum  reductum 143 


384  INDEX. 

PAGE 

Filter,  Beale's , 291 

Flasks,  measuring 20 

Float,  Erdman's 29 

Fluorescein  test  solution 366 

Fowler's  solution 165 

Gallein 366 

Gasometric  analyses 342 

Gay-Lussac's  burette 19 

General  principles  upon  which  volumetric  analysis  is  based 12 

Glacial  acetic  acid 76 

Glucose 259 

Glucosides 308 

Glue  and  salt  solution 243 

Glycerine 262 

Glycerol 262 

Glycyrrhetin . .  r 308 

Glycyrrhizin 308 

Goulard's  extract 124 

Graduated  cylinder 21 

Gramme,  the 15 

Gravimetric  method,  the , I 

Haines'  test,  for  sugar  in  urine. 335 

Haloid  salts 95 

Hardness  of  water 219 

permanent 220-224 

temporary 220 

Helianthin 363 

Holder  for  burettes 26 

Hydriodic  acid,  syrup  of in 

Hydrobromic  acid,  diluted 77 

Hydrochloric  acid 78 

diluted 79 

standard  V.  S.  of 40 

Hydrocyanic  acid -.. 117 

Senier's  method 118 

U.  S.  P.  method 119 

Hydrogen  dioxide 152,  200,  357 

peroxide 152,200,  357 


INDEX.  385 

PAGE 

Hydrogen  peroxide,  assay  of 154,  2O°,  357 

estimation  of  volume  strength  of.  .155,  200,  357 

Hydroxide  of  ammonium 46 

calcium 90 

potassium 43 

sodium 45 

Hydroxides,  alkaline 43 

Hypobromite  solution  for  urea 353 

Hy  pophosphite  of  calcium 148 

iron 149 

potassium 150 

sodium 151 

Hypophosphorous  acid 79,  146 

Hyposulphite  of  sodium 168 

decinormal  V.  S.  of .• 1 73 

Indicator,  defined 10 

requirements  of  a  good 360 

Indicators 10,  360 

Brazil-wood  T.  S , n,  368 

cochineal  T.  S 1 1,  368 

corallin  T.  S , 366 

eosin,  and  its  solution u,  366 

fluorescein,  and  its  solution n,  366 

gallein 366 

lacmoid,  and  lacmoid  paper 367 

litmus 10,  360 

methyl-orange 363 

test  solution n,  364 

phenacetolin 368 

phenolphthalein 362 

test  solution 10,  363 

rosolic  acid , . , 365 

test  solution 10,  366 

turmeric  tincture u,  369 

paper 369 

Indigo-carmine  test  for  sugar 335 

solution 243 

Indirect  oxidation,  analysis  by 161 

Interpretation  of  results  of  water  analyses 224 


386  INDEX. 


PAGE 


Instruments,  cleaning  of 27 

graduation  of 15 

correct  reading  of 28 

Iodide  of  iron,  saccharated 116 

syrup  of ,., 112 

by  sulphocyanate  method 114 

potassium 105 

Personnel  method 106 

sodium 107 

strontium 108 

zinc 108 

Iodine 175 

decinormal  V.  S.  of 162 

tincture  of 177 

lodometric  method  for  estimating  hydrogen  dioxide 200 

lodometry   172 

Ipecac  root 306 

fluid  extract  of , . , . .   304 

Iron  and  ammonium  citrate 188 

sulphate 192 

tartrate 188 

potassium  tartrate 188 

quinine  citrate. ,    189 

soluble .......  , 191 

strychnine  citrate 191 

acetate,  solution  of 196 

bromide,  syrup  of 117 

carbonate,  saccharated , 138 

chloride 184 

solution  of 185 

tincture  of 186 

citrate 1 86 

solution  of 187 

hypophosphite 149 

iodide,  saccharated 1 16 

syrup  of 112,  114 

nitrate,  solution  of 197 

phosphate,  soluble 188 

pyrophosphate,  soluble , 194 

reduced 143 


INDEX.  387 

PAGE 

Iron,  saccharated  carbonate 138 

iodide 116 

salts  (ferric) 183 

(ferrous) 128 

estimation  of,  by  K2Cr2O7 136 

2KMnO4 141 

sulphate 140-145 

subsulphate,  solution  of 198 

syrup  of  bromide 117 

iodide 112,  117 

tersulphate,  solution  of 199 

valerianate 195 

wire,    standardization    of    dichromate    and    permanganate 

solutions  with 132 

Kilogramme,  the 15 

Kingzett's  method  for  estimating  hydrogen  dioxide 200 

Koppeschaar's  solution 266 

Labarraque's  solution 181 

Lacmoid .  367 

paper 367 

Lactate  of  strontium 94 

Lactic  acid ...    30 

Lactometer 311 

Laudanum 300 

Law,  Boyle's 344 

Charles' 344 

Lead  subacetate  solution 1 24 

water 126 

Lemon-juice 77 

Lime,  chloride  of 178 

chlorinated 178 

valuation  of,  by  arsenous  acid 180 

juice 77 

Liquor  acidi  arsenosi   164 

calcis 90 

saccharatus 9i 

ferr:  acetatis. 196 

chloddi     ,..,:...,. 185 


388  INDEX. 

PAGE 

Liquor  ferri  citratis 187 

nitratis 197 

subsulphatis 198 

tersulphatis 199 

iodi  compositus 176 

plumbi  subacetatis 124 

potassae. .  > 44 

arsenitis 165 

sodae 45 

chloratae 181 

Lithium  benzoate 63 

bromide 101 

carbonate 51 

citrate 59 

salicylate 66 

Litmus  tincture. ... n,  360 

Litre,  the...., 15 

flask 20 

Loss  on  ignition 206 

Lugol's  solution 176 

Lunar  caustic 123 

Magnesia  mixture 84 

Magnesium  salts 95 

Malt  extracts,  diastasic  value  of 281 

Mandarin-orange 363 

Mayer's  solution 292 

Measuring-flask 20 

Melting-points  of  fats 251 

Meniscus 28 

Methyl-orange 363 

test  solution n,  364 

Milk 309 

Adam's  method  for  fat  in 314 

adulterations  of 313 

ash 317 

average  composition  of 309 

calculation  method  for  fat  in 316 

of  per  cent  of  added  water 317 

composition,  average 309 


INDEX.  389 

PAGE 

Milk  fat 314 

Werner-Schmid  method  for 313 

lactose 318 

milk  sugar 318 

reaction  of 310 

specific  gravity  of 310 

total  proteids  of 3 x 8 

solids  in 313 

Mineral  acids  in  vinegar  75 

Mitigated  caustic > 123 

Mohr's  burette 19 

foot-burette 19 

Molisch's  test  for  sugar  in  urine ,. . .  335 

Monsel's  solution 198 

Moore's  test  for  sugar  in  urine 334 

Moulded  caustic 123 

Murexid  test  for  uric  acid 330 

Muriatic  acid 78 

Naphthalamin-hydrochlorate  solution 214 

Naphthylammonium-chloride  solution 214 

Nessler's  solution 207 

Neutralization,  analysis  by 36 

Nitrate  of  barium 93 

iron,  solution .  197 

potassium  solution. 212 

silver 121 

diluted 123 

moulded 123 

standard  solution  of. 97 

Nitrates  in  water 211 

nitric  acid  in 350 

Nitric  acid  in  nitrates 350 

Nitrite  of  amyl 349 

ethyl 346 

sodium 350 

Nitrites  in  water 214 

Nitrite,  standard  solution  of,  for  water  analysis  215 

Nitrogen,  as  ammonia  211 

nitrates 2H 


3QO  INDEX. 

PAGE 

Nitrogen,  as  nitrites 214 

Nitrometer,  the 342 

estimation  of  carbonates  with 352 

Nitrous  ether 346 

Normal  solutions 4-8 

hydrochloric  acid  V.  S 40 

oxalic  acid  V.  S 39 

potassium  hydroxide  V.  S 71 

sodium  carbonate  V.  S 89 

hydroxide  V.  S 69 

sulphuric  acid  V.  S 41 

Nux- vomica  extract 296 

fluid  extract 298 

tincture k 298 

Nylander's  test  for  sugar  in  urine 334 

Oil  in  emulsions,  estimation  of 252 

Ointments,  estimation  of  fat  in 252 

Oleic  acid 246 

Oliver's  test  for  bile  in  urine 338 

Opium 301 

extract  of 298 

tincture  of 300 

Orange,  methyl 363 

Organic  and  volatile  matters  in  water 206 

salts  of  the  alkaline  metals 54 

Oxalic  acid 158 

decinormal  solution  of 40 

normal  solution  of 39 

Oxide  of  silver 123 

Oxidation,  analysis  by 127 

indirect,  analysis  by. 161 

Oxidimetry 127 

Oxygen-consuming  power  of  water 216 

Pancreatic  extracts,  diastasic  value  of 281 

Pepsin <., 275 

valuation  of 277,  278 

Percentages,  how  found 31 

Permanganate  of  potassium,  alkaline  solution  of 208 


INDEX.  391 

PAGE 

Permanganate  of  potassium,  centinormal  V.  S.  of 131 

decinormal  V.  S.  of 131 

Peroxide  of  barium 157 

hydrogen 152-154,  200,  357 

Pettenkofer's  test  for  bile  in  urine « 338 

Phenacetolin : , 368 

Phenol * 266-272 

Phenolphthalein 362 

solution  of 10,  363 

Phosphates  in  urine  327 

water , 219 

Phosphoric  acid 82 

by  Stolba's  method 84 

as  ammonio-magnesian  phosphate 84 

Picric-acid  test  for  sugar  in  urine 334 

Pipettes 21 

nipple 22 

Porrier's  orange  III 363 

Potassa » 43 

solution  of 44 

Potassio-ferric  tartrate 188 

Potassium  acetate 61 

and  sodium  tartrate 57 

arsenite,  solution  of 165 

bicarbonate 49 

bitartrate 58 

bromide , 101 

bichromate,  decinormal  V.  S.  of 129 

carbonate 48 

chloride 109 

chromate,  solution  of.    n,  206 

citrate 60 

cyanide „ 120 

dichromate,  decinormal  V.  S.  of , 129 

tests  for  the  purity  of 129 

ferricyanide  T.  S n 

hydroxide,  centinormal  V.  S.  of 71 

normal  V.  S.  of 60 

iodide  105 

Personne's  method. .  106 


392  INDEX. 

PAGB 

Potassium  nitrate  solution,  for  water  analysis 212 

permanganate,  centinormal  V.  S.  of 131 

decinormal  V.  S.  of 131 

standardization  of,  with  iron 132 

oxalic  acid 133 

solution  of,  for  determining  the  oxy- 
gen-consuming power  of  water 217 

sulphocyanate  V.  S 113 

sulphite 167 

tartrate 55 

Precipitation,  analysis  by  96 

Preservation  of  alkaline  solutions,  bottle  for 69 

Pus  in  urine 333 

Pyrophosphate  of  iron,  soluble 194 

Qualitative  analysis I 

Quantitative  analysis   I 

Quinine,  in  citrate  of  iron  and  quinine 189 

Reaction  of  milk 310 

urine 322 

Reading  of  instruments 28 

Reagents  and  test  solutions 369 

Reduced  iron 143 

Reduction,  analysis  by 172 

Residual  titration 9 

Resin,  estimation  of,  in  drugs 306 

Resorcin-phthalein 366 

Results,  interpretation  of 224 

Retitration 9 

Rochelle  salt 57 

Rosolic  acid 365 

solution  of n,  366 

Saccharated  ferrous  carbonate 138 

iodide 116 

Salicin 308 

Salicylate  of  lithium 66 

sodium 67 

Salt  solution,  acidified 244 


^ 


INDEX.  39 


&if5'$£& 


Saturation,  analysis  by 38 

Semi-normal  solutions. 9 

Separator 293 

Set  solution , 4 

Silver  carbonate  test,  for  uric  acid 330 

estimation  of,  by  sulphocyanate 124 

nitrate 121 

diluted 123 

moulded 123 

solution,  for  water  analysis 206 

Soap,  analysis  of 248 

solution,  for  determining  hardness  of  water 221 

Soda 45 

solution  of 45 

Sodium  acetate 62 

and  potassium  tartrate 57 

benzoate 64 

bicarbonate 50 

bisulphite 168 

bromide 102 

carbonate 49 

exsiccated 50 

normal  V.  S 89 

solution,  for  water  analysis 208 

chloride no 

decinormal  V.  S 122 

purification  of 122 

hydroxide 45 

normal  V.  S 71 

hypophosphite 151 

hyposulphite 168 

iodide 107 

nitrite , 350 

solution 215 

salicylate 67 

sulphite 166 

thiosulphate 168 

tungstate  test  for  albumen 331 

Solution,  alkaline  permanganate 208 

ammonium  chloride 208 


394  INDEX. 

PAGE 

Solution,  chlorinated  soda 181 

ferric  chloride 185 

citrate iSS 

nitrate 197 

subsulphate 198 

tersulphate 199 

Fowler's 165 

Labarraque's 181 

Lugol's 176 

Monsel's 198 

silver  nitrate,  for  water  analysis 206 

decinormal 97 

soap,  for  estimating  hardness  of  water 221 

sodium  carbonate,  for  water  analysis 208 

normal  V.  S ...  89 

nitrite 215 

subsulphate  of  iron 198 

sulphanilic  acid 214 

tersulphate  of  iron 199 

Solutions,  centinormal 8 

decinormal 8 

empirical « 9 

normal 4-8 

semi-normal 9 

"set" 4 

standard 4 

"  standarized  " 4 

Soxhlet's  extraction  apparatus   253 

Specific  gravity  of  milk 310 

urine 324 

Spirit  of  ammonia  47 

aromatic 352 

nitrous  ether 346 

Squibb's  urea  apparatus 355 

Standard  solutions 4 

Standards  for  determining  the  quality  of  water 231 

Starch,  estimation  of 255-258 

Statement  of  water  analysis 224 

Strontium  bromide 103 

iodide 108 


INDEX.  395 

PAGE 

Strontium  lactate 94 

Strychnine,  in  citrate  of  iron  and  strychnine 191 

Subacetate  of  lead  solution 124 

Sugar  in  urine 334 

bismuth  test  for 334 

Einhorn's  saccharometer  test 336 

Haines'  test 336 

indigo-carmine  test 335 

Molisch's  test 334 

Moore's  test 334 

Ny lander's  test 334 

picric-acid  test 334 

quantitative  estimation  of . ,  335 

Trommer's  test 335 

Support  for  burettes 25 

Sulphanilic-acid  test  solution 214 

Sulphates  in  urine 327 

gravimetric  estimation  of 328 

volumetric  estimation  of 328 

Sulphocyanate  method  for  ferrous  salts 114 

solution e 113 

Sulphite  of  potassium , 167 

sodium 1 66 

Sulphuric  acid 86 

aromatic 87 

diluted. . . '. 87 

Sulphurous  acid 165 

Syrup  of  ferrous  bromide 117 

iodide 112.  117 

hydriodic  acid in 

lime 91 

Table,  acetic  acid 75 

for  ascertaining  the  percentage  of  alcohol 240 

correcting  the  sp.  gr.  of  milk,  according  to  the  temper- 
ature     312 

of  the  elementary  substances xvii 

substances  estimated  by  precipitation 125 

substances,  which   may  be  estimated  by  oxidation  with 

K2Cr2O7  or  2KMnO4 .  160 


396  INDEX. 

PAGE 

Table,  of  substances,  estimated  by  iodine 171 

sodium  thiosulphate 201 

showing  behavior  of  some  alkaloids  with  indicators 289 

showing  approximate  normal  factors,  etc.,  for  the  acids. .     88 
showing  approximate  normal  factors,  etc.,  for  the  alkalies, 

alkaline  earths,  and  acids 35 

showing  approximate  normal  factors,  etc.,  for  the  organic 

salts  of  the  alkalies 68 

showing  factors  for  various  alkaloids  when  titrating  with 

N 

—  acid  or  alkali 200 

20 

showing  composition  of  the  milk  of  different  animals. .  . .  310 

showing  average  composition  of  normal  urine 323 

showing   contraction  and  expansion  of  water  at  various 

temperatures., 16 

showing  relationship  of  the  lactometer  indication  to  the 

sp.gr 311 

showing  volume  of  .001  gm.  of  CO2  at  various  tempera- 
tures     237 

Tannic  acid,  estimation  of 242,  243 

Tannin,  estimation  of 242,  243 

Tartrate  of  antimony  and  potassium 169 

iron  and  ammonium 188 

potassium 188 

potassium 55 

and  sodium 57 

solution,  alkaline,  for  sugar 259 

Tartrates,  estimation  of 54 

Tartar  emetic 169 

Tartaric  acid 87 

Tersulphate-of-iron  solution 199 

Test-mixer 21 

Test  solutions  and  reagents 369 

Thiosulphate  of  sodium 168 

decinormal  V.  S.  of 173 

Tincture  of  iodine 117 

test  for  bile  in  urine 339 

turmeric 369 

Titrate,  to 9 

Titrated  solution 4 


INDEX.  397 

PAGE 

Titration,  backward 9 

residual ° 9 

Total  acidity  of  urine • 32^ 

proteids  in  milk 318 

solids,  and  added  water,  in  milk  313 

in  urine 325 

Trommer's  test  for  sugar  in  urine .  335 

Tropaeolin  D 366 

Turmeric  paper 369 

tincture 1 1,  369 

Ultzmann's  test  for  bile  in  urine 339 

Urates 329 

Urea,  estimation  of 329 

by  Doremus'  ureometer 353 

gas  tube  . .    354 

Squibb's  urea  apparatus 355 

Ureometer 353 

Uric  acid 329 

qualitative  tests  for 330 

quantitative  estimation  of 336 

murexid  test  for 330 

silver-carbonate  test  for 330 

Urinary  deposits 339 

chemical  examination  of 339 

microscopical  examination  of ...  339 

Urine,  abnormal  constituents  of 330 

acidulated  brine  test  for  albumen  in 332 

albumen  in 330 

detection  of,  by  boiling 330 

nitric-acid  test 331 

ferrocyanide  test 331 

picric-acid  test 331 

albumen  in,  detection  of,  by  potassio-mercuric-iodide  test  331 

sodium-tungstate  test 332 

quantitative  estimation  of,  by  Esbach's  albu- 

minometer 332 

average  composition  of , 223 

bile  in,  detection  of,  by  Gmelin's  test 338 


398  INDEX. 


bile  in,  detection  of,  by  Oliver's  test  ....................  338 

Pettenkofer's  test  ................  336 

tincture-of-iodine  test  ............  339 

Ultzmann's  test  ................  339 

bismuth  test,  for  sugar  in  .............................  334 

blood  in  ..............................................  333 

chlorides  in.  ...   ......................................  326 

fermentation  test,  for  sugar  in  ........................   336 

ferrocyanide  test,  for  albumen  in  .......................   331 

Gmelin's  test,  for  bile  in  .............................   338 

gravimetric  estimation  of  sulphates  in  ...................   328 

Haines'  test,  for  sugar  in  ..............................   335 

indigo-carmine  test,  for  sugar  in  .......................   335 

Molisch's  test,  for  sugar  in  ............................  335 

Moore's  test,  for  sugar  in  .............................  334 

murexid  test,  for  uric  acid  in  .................  .........  330 

Nylander's  test,  for  sugar  in  ...........................   334 

nitric-acid  test,  for  albumen  in  ....................    ...  331 

normal  ...............................................   322 

Oliver's  test,  for  bil    in  ...............................   338 

Pettenkofer's  test,  for  bile  in  .........................  338 

phosphates  in  ........................................  327 

picric-acid  test,  for  sugar  in  ...........................  334 

albumen  in  .........................  331 

potassio-mercuric-iodide  test,  for  albumen  in  ............  332 

pus  in  ...............................................   333 

reaction  of  .........................................   322 

silver-carbonate  test,  for  uric  acid  ......................  330 

sodium-tungstate  test,  for  albumen  in  ..................   332 

specific  gravity  of  .....................................  324 

sugar  in  .............................................  324 

sulphates  in  ..........................................   327 

total  acidity  of  .............................  .  .  .........   328 

solids  of  ........................................   325 

Trommer's  test,  for  sugar  in  ...........................   335 

tincture-of-iodine  test,  for  bile  in  ......................   339 

Ultzmann's  test,  for  bile  in  ......  ,  .....................   339 

urates  in  ............................................   329 

urea  in  ..............................................   329 

uric  acid  in  ..........................................   329 


INDEX.  399 

PAGE 

Urine,  volumetric  estimation  of  chlorides  in 326 

sulphates  in 328 

Urinometer 324 

Use  of  apparatus •••  27 

Valerianate  of  iron 195 

Valuation  of  pepsin,  Hartley's  method 278 

U.  S.  P.  method 277 

Vinegar - 74 

estimation  of  mineral  acids  in 75 

Volhard's  method  for  ferrous  iodide 112 

solution 113 

Volume  strength  of  hydrogen  dioxide 155 

Volumetric  estimation  of  alkaloids 285 

instruments,  how  graduated 15 

method,  the 2 

solutions 4 

centinormal 8 

decinormal 8 

double-normal 9 

normal 4-8 

seminormal 9 

solution  of  alkaline  permanganate 208 

arsenous  acid,  decinormal 181 

bromine,  decinormal 262 

dichromate 1 29 

hydrochloric  acid,  normal  .., 40 

iodine,  decinormal 162 

mercuric  potassium  iodide 292 

oxalic  acid,  decinormal 40 

normal 39 

N 
permanganate,  — 243 

decinormal 131 

potassium  dichromate,  decinormal 129 

hydroxide,  centinormal  71 

normal 69 

silver  nitrate,  decinormal. 97 

sodium  carbonate,  normal , 89 

chloride,  decinormal 122 


4OO  INDEX. 

PAGE 

Volumetric  solution  of  sodium  hyposulphite 173 

thiosulphate 173 

Water,  albuminoid  ammonia  in 210,  228 

Water,  ammonia 46 

in 207,  227 

free ..  . .  208 

analysis  of,  sanitary 202 

chlorine  in 206,  226 

collection  of  sample  of 202 

color  of. ...  : 203,  225 

hardness  of 219,  224 

interpretation  of  results  of  analysis  of 224 

loss  on  ignition 205 

nitrogen  as  nitrates  in 211,  228 

nitrites  in 214 

odor 203,  225 

organic  and  volatile  matter  in 205 

oxygen-consuming  power  of 216 

permanent  hardness  of 220,  224 

phosphates  in 217 

reaction  of 204 

statement  of  analysis  of „ 224 

suspended  matter 204 

temporary  hardness  of 220 

total  solids  in 204,  225 

Weights  and  measures  used  in  volumetric  analysis 15 

Zinc  bromide ...   104 

chloride no 

iodide..  .  ioS 


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Phelps's  Practical  Marine  Surveying Svo,  2  50 

Very's  Navies  of  the  World 8vo,  half  morocco,  3  50 

Bourne's  Screw  Propellers, , ..,.,..,.,.,,,,.,,,  ,4to,  5  00 

2 


Hunter's  Port  Charges 8vo,  half  morocco,  $13  00 

*  Dredge's  Modern  French  Artillery 4to,  half  morocco,  20  00 

"          Record   of   the   Transportation    Exhibits    Building, 

World's  Columbian  Exposition  of  1893.. 4to,  half  morocco,  15  00 

Mercur's  Elements  of  the  Art  of  War 8vo,  4  00 

Attack  of  Fortified  Places 12mo,  200 

Chase's  Screw  Propellers 8vo,  3  00 

Winthrop's  Abridgment  of  Military  Law 12mo,  2  50 

De  Brack's  Cavalry  Outpost  Duties.     (Carr.). . .  .18mo,  morocco,  2  00 

Cionkhite's  Gunnery  for  Non-com.  Officers 18mo,  morocco,  2  00 

Dyer's  Light  Artillery 12mo,  3  00 

Sharpe's  Subsisting  Armies 18mo,  1  25 

"                              "       18mo,  morocco,  1  50 

Powell's  Army  Officer's  Examiner 12mo,  4  00 

Hoff's  Naval  Tactics 8vo,  1  50 

Bruff ' s  Ordnance  and  Gunnery 8vo,  6  00 

ASSAYING. 

SMELTING — ORE  DRESSING— ALLOYS,  ETC. 

Furman's  Practical  Assaying 8vo,  3  00 

Wilson's  Cyanide  Processes l-2rno,  1  50 

Fletcher's  Quant.  Assaying  with  the  Blowpipe..  12mo,  morocco,  1  50 

Ricketts's  Assaying  and  Assay  Schemes 8vo,  300 

*  Mitchell's  Practical  Assaying.     (Crookes.) 8vo,  10  00 

Thurston's  Alloys,  Brasses,  and  Bronzes 8vo,  2  50 

Kimhardt's  Ore  Dressing 8vo,  1  50 

O'Driscoll's  Treatment  of  Gold  Ores 8vo,  2  00 

ASTRONOMY. 

PRACTICAL,  THEORETICAL,  AND  DESCRIPTIVE. 

Michie  and  Harlow's  Practical  Astronomy 8vo,  3  00 

White's  Theoretical  and  Descriptive  Astronomy 12mo,  2  -00 

Doolittle's  Practical  Astronomy Svo,  4  00 

Craig's  Azimuth   4to,  3  50 

Elements  of  Geodesy 8vo,  '  2  50 


BOTANY. 

GARDENING  FOR  LADIES,  ETC. 

Westermaier's  General  Botany.     (Schneider.) 8vo,  $2  00 

Thome's  Structural  Botany 18mo,  2  25 

Baldwin's  Orchids  of  New  England Svo,  1  50 

Loudon's  Gardening  for  Ladies.     (Downing.) 12nio,  1  50 

BRIDGES,  ROOFS,   Etc. 

CANTILEVER — HIGHWAY — SUSPENSION. 

Boiler's  Highway  Bridges 8vo,  2  00 

*  "       The  Thames  River  Bridge 4to,  paper,  5  00 

Burr's  Stresses  in  Bridges Svo,  3  50 

Merriman  &  Jacoby's  Text-book  of  Roofs  and  Bridges.     Part 

I.,  Stresses .8vo,  250 

Merriman  &  Jacoby's  Text-book  of  Roofs  and  Bridges.     Part 

II.,  Graphic  Statics Svo,  2  50 

Merrimau  &  Jacoby's  Text-book  of  Roofs  and  Bridges.     Part 

III.,  Bridge  Design 8vo,  5  00 

Merriman  &  Jacoby's  Text- book  of  Roofs  and  Bridges.     Part 

IV.,    Continuous,    Draw,    Cantilever,    Suspension,    and 

Arched  Bridges , (In  preparation}. 

Crehore's  Mechanics  of  the  Girder Svo,  5  00 

Du  Bois's  Strains  in  Framed  Structures ,4to,  10  00 

Greene's  Roof  Trusses Svo,  1  25 

Bridge  Trusses 8vo,  250 

"        Arches  in  Wood,  etc Svo,  2  50 

Waddell's  Iron  Highway  Bridges Svo,  4  00 

Wood's  Construction  of  Bridges  and  Roofs Svo,  2  00 

Foster's  Wooden  Trestle  Bridges 4to,  5  00 

*  Morison's  The  Memphis  Bridge Oblong  4to,  10  00 

Johnson's  Modern  Framed  Structures 4to,  10  00 

CHEMISTRY. 

QUALITATIVE — QUANTITATIVE — ORGANIC — INORGANIC,  ETC. 

Fresenius's  Qualitative  Chemical  Analysis.    (Johnson.) Svo,       4  00 

"         Quantitative  Chemical  Analysis.    (Allen.) Svo,      6  00 

"  "  "  "  (Boltoii.) Svo,       1  50 

4 


Crafts's  Qualitative  Analysis.     (Schaeffer.) 12rno,    $1  50 

Perkins's  Qualitative  Analysis 12mo,  1  00 

Thorpe's  Quantitative  Chemical  Analysis 18mo,  1  50 

Classen's  Analysis  by  Electrolysis.     (Herrick.) 8vo,  *    3  00 

Stockbridge's  Rocks  and  Soils 8vo,  2  50 

O'Brine's  Laboratory  Guide  to  Chemical  Analysis 8vo,  2  00 

Mixter's  Elementary  Text-book  of  Chemistry 12mo,  1  50 

Wulling's  Inorganic  Phar.  and  Med.  Chemistry 12mo,  2  00 

Mandel's  Bio-chemical  Laboratory 12mo,  1  50 

Austen's  Notes  for  Chemical  Students 12mo, 

Schimpf's  Volumetric  Analysis 12mo,  2  50 

Hammarsten's  Physiological  Chemistry  (Maudel.) 8vo,  4  00 

Miller's  Chemical  Physics 8vo,  2  00 

Pinner's  Organic  Chemistry.     (Austen.) 12mo,  1  50 

Kolbe's  Inorganic  Chemistry 12mo,  1  50 

Ricketts  and  Russell's  Notes  on   Inorganic  Chemistry  (Non- 
metallic) Oblong  8vo,  morocco,  75 

Drechsel's  Chemical  Reactions.    (Merrill.) 12mo,  1  25 

Adriance's  Laboratory  Calculations 12mo,  1  25 

Troilius's  Chemistry  of  Iron 8vo,  2  00 

Allen's  Tables  for  Iron  Analysis Svo, 

Nichols's  Water  Supply  (Chemical  and  Sanitary) Svo,  2  50 

Mason's         «<           "               "            "          "          Svo,  5  00 

Spencer's  Sugar  Manufacturer's  Handbook .  12mo,  morocco  flaps,  2  00 

Wiechmanu's  Sugar  Analysis. 8vo,  2  50 

' '            Chemical  Lecture  Notes 12mo,  3  00 

DRAWING. 

ELEMENTARY — GEOMETRICAL — TOPOGRAPHICAL. 
Hill's  Shades  and  Shadows  and  Perspective. . .  .(In  preparation) 

Mahan's  Industrial  Drawing.    (Thompson.) 2  vols.,  Svo,  3  50 

MacCord's  Kinematics Svo,  5  00 

Mechanical  Drawing Svo,  400 

"         Descriptive  Geometry 8vo,  3  00 

Reed's  Topographical  Drawing.     (II.  A.) 4to,  5  00 

Smith's  Topographical  Drawing.     (Macmillan.) — Svo,  2  50 

Warren's  Free-hand  Drawing    12ino,  1  00 

5 


Warren's  Drafting  Instruments 4 12mo,  $1  25 

"  Projection  Drawing 12mo,  150 

"  Linear  Perspective 12mo,  100 

"'  Plane  Problems , 12mo,  125 

"  Primary  Geometry 12mo,  75 

"  Descriptive  Geometry 2  vols.,  8vo,  3  50 

"  Problems  and  Theorems 8vo,  2  50 

"  Machine  Construction 2  vols.,  8vo,  7  50 

"  Stereotomy — Stone  Cutting 8vo,  250 

"  Higher  Linear  Perspective  8vo,  3  50 

"  Shades  and  Shadows 8vo,  300 

Whelpley's  Letter  Engraving 12mo,  2  00 

ELECTRICITY  AND  MAGNETISM. 

ILLUMINATION— BATTERIES— PHYSICS. 

*  Dredge's  Electric  Illuminations. . .  .2  vols.,  4to,  half  morocco,  25  00 

Vol.  II 4to,  750 

Niaudet's  Electric  Batteries.     (Fishback.) .  .12mo,  2  50 

Anthony  and  Brackett's  Text-book  of  Physics 8vo,  4  00 

Cosmic  Law  of  Thermal  Repulsion 18mo,  75 

Thurston's  Stationary  Steam  Engines  for  Electric  Lighting  Pur- 

-  poses 12mo,  1  50 

Michie's  Wave  Motion  Relating  to  Sound  and  Light, 8vo,  4  00 

Barker's  Deep-sea  Souu4mgs 8vo,  2  00 

Holman's  Precision  of  Measurements 8vo,  2  00 

Tillman's  Heat 8vo,  1  50 

Gilbert's  De-magnete.     (Mottelay.) 8vo,  2  50 

Benjamin's  Voltaic  Cell 8vo,  3  00 

Reagan's  Steam  and  Electrical  Locomotives 12mo  2  00 

ENGINEERING. 

CIVIL — MECHANICAL — SANITARY,  ETC. 

*  Trautwine's  Cross-section Sheet,  25 

Civil  Engineer's  Pocket-book.  ..12m o,  mor.  flaps,  500 

"            Excavations  and  Embankments 8vo,  2  00 

*  "            Laying  Out  Curves 12mo,  morocco,  2  50 

Hudson's  Excavation  Tables.    Vol.  II 8vo,  1  00 

6 


Searles's  Field  Engineering 12mo,  morocco  flaps,  $3  00 

"       Railroad  Spiral 12mo,  morocco  flaps,  1  50 

Godwin's  Railroad  Engineer's  Field-book.  12mo,  pocket-bk.  form,  2  50 

Butts's  Engineer's  Field-book 12mo,  morocco,  2  50 

Gore's  Elements  of  Goodesy 8vo,  2  50 

Wellington's  Location  of  Railways. 8vo,  5  00 

*  Dredge's  Penn.  Railroad  Construction,  etc.  .  .  Folio,  half  mor.,  20  00 
Smith's  Cable  Tramways 4to,  2  50 

"Wire  Manufacture  and  Uses 4to,  3  00 

Mahan's  Civil  Engineering.      (Wood.) 8vo,  5  00 

Wheeler's  Civil  Engineering 8vo,  4  00 

Mosely's  Mechanical  Engineering.     (Mahan.) 8vo,  5  00 

Johnson's  Theory  and  Practice  of  Surveying 8vo,  4  00 

Stadia  Reduction  Diagram.  .Sheet,  22£  X  28£  inches,  50 

*  Drinker's  Tunnelling 4to,  half  morocco,  25  00 

Eissler's  Explosives — Nitroglycerine  and  Dynamite 8vo,  4  00 

Foster's  Wooden  Trestle  Bridges 4to,  5  00 

Ruffner's  Non-tidal  Rivers 8vo,  1  25 

Greene's  Roof  Trusses 8vo,  1  25 

"  Bridge  Trusses 8vo,  2  50 

Arches  in  Wood,  etc 8vo,  250 

Church's  Mechanics  of  Engineering — Solids  and  Fluids. ..  .8vo,  6  00 

"  Notes  and  Examples  in  Mechanics 8vo,  2  00 

Howe  s  Retaining  Walls  (New  Edition.) 12mo,  1  25 

Wegmann's  Construction  of  Masonry  Dams 4to,  5  00 

Thurston's  Materials  of  Construction 8vo,  5  00 

Baker's  Masonry  Construction 8vo,  5  00 

"  Surveying  Instruments 12mo,  3  00 

Warren's  Stereotomy— Stone  Cutting 8vo,  2  50 

Nichols's  Water  Supply  (Chemical  and  Sanitary) 8vo,  2  50 

Mason's  "  "  "  "  "  8vo,  500 

Gerhard's  Sanitary  House  Inspection 16mo,  1  00 

Kirkwood's  Lead  Pipe  for  Service  Pipe 8vo,  1  50 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  00 

Howard's  Transition  Curve  Field-book 12mo,  morocco  flap,  1  50 

Crandail's  The  Transition  Curve 12mo,  morocco,  1  50 

7 


Cramkll's  Earthwork  Tables    8vo,  $1  50 

Pattern's  Civil  Engineering 8vo,  7  50 

"       Foundations 8vo,  5  00 

Carpenter's  Experimental  Engineering  8vo,  6  00 

Webb's  Engineering  Instruments 12mo,  morocco,  1  00 

Black's  U.  S.  Public  Works 4to,  5  00 

Merriman  and  Brook's  Handbook  for  Surveyors.  .  .  .12mo,  mor.,  2  00 

Merriman's  Retaining  Walls  and  Masonry  Dams 8vo,  2  00 

"          Geodetic  Surveying 8vo,  200 

Kiersted's  Sewage  Disposal 12rno,  1  25 

Siebert  and  Biggin's  Modern  Stone  Cutting  and  Masonry. .  .8vo,  1  50 

Kent's  Mechanical  Engineer's  Pocket-book 12mo,  morocco,  5  00 

HYDRAULICS. 

WATER-WHEELS — WINDMILLS — SERVICE  PIPE — DRAINAGE,  ETC. 

Weisbach's  Hydraulics.     (Du  Bois.) 8vo,  5  00 

Merrimau's  Treatise  on  Hydraulics 8vo,  4  00 

Ganguillet&  Kutter'sFlow  of  Water.  (Hering&  Trautwine  ).8vo,  4  00 

Nichols's  Water  Supply  (Chemical  and  Sanitary) 8vo,  2  50 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  00 

Ferrel's  Treatise  on  the  Winds,  Cyclones,  and  Tornadoes. . .  8vo,  4  00 

Kirkwood's  Lead  Pipe  for  Service  Pipe  8vo,  1  50 

Ruffner's  Improvement  for  Non-tidal  Rivers 8vo,  1  25' 

Wilson's  Irrigation  Engineering 8vo,  4  00 

Bovey's  Treatise  on  Hydraulics. . . , . 8vo,  4  00 

Wegmaun's  Water  Supply  of  the  City  of  New  York 4to,  10  00 

Hazeu's  Filtration  of  Public  Water  Supply 8vo,  2  00 

Mason's  Water  Supply — Chemical  and  Sanitary 8vo,  5  00 

Wood's  Theory  of  Turbines , 8vo,  2  50 

MANUFACTURES. 

ANILINE — BOILERS — EXPLOSIVES — IRON — SUGAR — WATCHES  — 
WOOLLENS,  ETC. 

Metcalfe's  Cost  of  Manufactures 8vo,  5  00 

Metcalf 's  Steel  (Manual  for  Steel  Users) I2ino,  2  00 

Allen's  Tables  for  Iron  Analysis 8vo, 

8 


West's  American  Foundry  Practice 12mo,  $2  50 

"      ."Moulder's  Text-book  12mo,  2  50 

Spencer's  Sugar  Manufacturer's  Handbook. . .  .12mo,  rnor.  flap,  2  00 

Wiechinaun's  Sugar  Analysis 8vo,  2  50 

Beaumont's  Woollen  and  Worsted  Manufacture ISino,  1  50 

*  Reisig's  Guide  to  Piece  Dyeing 8vo,  25  00 

Eissler's  Explosives,  Nitroglycerine  and  Dynamite 8vo,  4  00 

Reimann's  Aniline  Colors.     (Crookes.) 8vo,  2  50 

Ford's  Boiler  Making  for  Boiler  Makers 18mo,  1  00 

Thurston's  Manual  of  Steam  Boilers 8vo,  5  00 

Booth's  Clock  and  Watch  Maker's  Manual 12mo,  2  00 

Holly's  Saw  Filing 18mo,  75 

Svedelius's  Handbook  for  Charcoal  Burners 12mo,  1  50 

The  Lathe  and  Its  Uses 8vo,  600 

Woodbury's  Fire  Protection  of  Mills 8vo,  2  50 

Bolland's  The  Iron  Founder 12mo,  2  50 

Supplement 12mo,  250 

"        Encyclopaedia  of  Founding  Terms 12mo,  3  00 

Bouvier's  Handbook  on  Oil  Painting 12mo,  2  00 

Steven's  House  Painting 18mo,  '  75 

MATERIALS  OF  ENGINEERING. 

STRENGTH — ELASTICITY — RESISTANCE,  ETC. 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  00 

Vol.  I.,  Non-metallic 8vo,  200 

Vol.  II.,  Iron  and  Steel 8vo,  3  50 

Vol.  III.,  Alloys,  Brasses,  and  Bronzes 8vo,  2  50 

Thurstou's  Materials  of  Construction 8vo,  5  00 

Baker's  Masonry  Construction 8vo,  5  00 

Lanza's  Applied  Mechanics. , 8vo,  7  50 

"        Strength  of  Wooden  Columns 8vo,  paper,  50 

Wood's  Resistance  of  Materials 8vo,  2  00 

Weyrauch's  Strength  of  Iron  and  Steel.    (Du  Bois.) 8vo,  1  50 

Burr's  Elasticity  and  Resistance  of  Materials 8vo,  5  00 

Merrimau's  Mechanics  of  Materials . . , 8vo,  4  00 

Church's  Mechanic's  of  Engineering — Solids  and  Fluids 8vo,  6  00 

9 


Beardslee  aud  Kent's  Strength  of  Wrought  Iron 8vo,  $1  50 

Hatfield's  Transverse  Strains 8vo,  5  00 

Du  Bois's  Strains  in  Framed  Structures 4to,  10  00 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  00 

Bovey's  Strength  of  Materials 8vo,  7  50 

Spaldiug's  Roads  and  Pavements 12mo,  2  00 

Rockwell's  Roads  and  Pavements  in  France 12mo,  1  25 

Byrne's  Highway  Construction 8vo,  5  00 

Pattou's  Treatise  on  Foundations 8vo,  5  00 

MATHEMATICS. 

CALCULUS — GEOMETRY — TRIGONOMETRY,  ETC. 

Rice  and  Johnson's  Differential  Calculus 8vo,  3  50 

Abridgment  of  Differential  Calculus 8vo,  1  50 

Differential  and  Integral  Calculus,  > 

2  vols.  in  1,  12mo,  2  50 

Johnson's  Integral  Calculus 12mo,  1  50 

"        Curve  Tracing 12mo,  1  00 

"        Differential  Equations — Ordinary  and  Partial 8vo,  3  50 

"        Least  Squares 12mo,  1  50 

Craig's  Linear  Differential  Equations 8vo,  5  00 

Merriman  and  Woodward's  Higher  Mathematics 8vo, 

Bass's  Differential  Calculus 12mo, 

Halsted's  Synthetic  Geometry 8vo,  1  50 

"       Elements  of  Geometry 8vo,  175 

Chapman's  Theory  of  Equations 12mo,  1  50 

^Merriinan's  Method  of  Least  Squares 8vo,  2  00 

Compton's  Logarithmic  Computations 12mo,  1  50 

Davis's  Introduction  to  the  Logic  of  Algebra 8vo,  1  50 

Warren's  Primary  Geometry 12mo,  75 

Plane  Problems 12mo,  125 

"        Descriptive  Geometry 2  vols.,  8vo,  3  50 

"        Problems  and  Theorems 8vo,  250 

"        Higher  Linear  Perspective 8vo,  3  50 

"        Free-hand  Drawing 12ino,  100 

"        Drafting  Instruments 12mo,  1  25 

10 


Warren's  Projection  Drawing 12mo,  $1  50 

"  Linear  Perspective 12mo,  1  00 

Plane  Problems 12mo,  125 

Searles's  Elements  of  Geometry 8vo,  1  50 

Brigg's  Plane  Analytical  Geometry 12mo,  1  00 

Wood's  Co-ordinate  Geometry 8vo,  2  00 

Trigonometry 12mo,  100 

Maban's  Descriptive  Geometry  (Stone  Cutting) 8vo,  1  50 

Woolf  s  Descriptive  Geometry Royal  8vo,  3  00 

Ludlow's  Trigonometry  witb  Tables.  (Bass.) 8vo,  3  00 

Logaritbmic  and  Otber  Tables.  (Bass.) 8vo,  2  00 

Baker's  Elliptic  Functions 8vo,  1  50 

Parker's  Quadrature  of  the  Circle 8vo,  2  50 

Totten's  Metrology 8vo,  2  50 

Ballard's  Pyramid  Problem 8vo,  1  50 

Barnard's  Pyramid  Problem 8vo,  1  50 

MECHANICS-MACHINERY. 

TEXT-BOOKS  AND  PRACTICAL  WORKS. 

Dana's  Elementary  Mechanics 12mo,  1  50 

Wood's          "                 "           '.12mo,  125 

"               "                 "           Supplement  and  Key 125 

Analytical  Mechanics 8vo,  300 

Michie's  Analytical  Mechanics 8vo,  4  00 

Merriman's  Mechanics  of  Materials .8vo,  4  00 

Church's  Mechanics  of  Engineering. 8vo,  6  00 

"        Notes  and  Examples  in  Mechanics 8vo,  2  00 

Mosely's  Mechanical  Engineering.     (Mahan.) 8vo,  5  00 

Weisbach's    Mechanics    of   Engineering.     Vol.    III.,    Part  I., 

Sec.  I.     (Klein.) 8vo,  500 

Weisbach's  Mechanics    of  Engineering.     Vol.   III.,    Part  I., 

Sec.  II.     (Klein.) 8vo,  500 

Weisbach's  Hydraulics  and  Hydraulic  Motors.    (Du  Bois.)..8vo,  5  00 

•*'•       Steam  Engines.     (Du  Bois.) 8vo,  500 

Lanza's  Applied  Mechanics .8vo,  7  50 

11 


Crehore's  Mechanics  of  the  Girder ..,*....*..* 8Vo,  $5  00 

MacCord's  Kinematics .J. . .  .8vo,  5  00 

Thurston's  Friction  and  Lost  Work 7". 8vo,  3  00 

The  Animal  as  a  Machine 12mo,  1  00 

Hall's  Car  Lubrication 12mo,  1  00 

Warren's  Machine  Construction 2  vols.,  8vo,  7  50 

Chordal's  Letters  to  Mechanics .  12mo,  2  00 

The  Lathe  and  Its  Uses 8vo,  6  00 

Cromwell's  Toothed  Gearing 12mo,  1  50 

Belts  and  Pulleys 12mo,  1  50 

Du  Bois's  Mechanics.     Vol.  I.,  Kinematics 8vo,  3  50 

Vol.11.,  Statics 8vo,  400 

Vol.  III.,  Kinetics 8vo,  350 

Dredge's     Trans.     Exhibits     Building,      World     Exposition, 

4to,  half  morocco,  15  00 

Flather's  Dynamometers 12mo,  200 

Rope  Driving 12mo,  200 

Richards's  Compressed  Air 12mo,  1  50 

Smith's  Press-working  of  Metals 8vo,  ?,  00 

Holly's  Saw  Filing 18nio,  15 

Fitzgerald's  Boston  Machinist 18mo,  1  00 

Baldwin's  Ste^tn  Heating  for  Buildings 12mo,  2  50 

Metcalfe's  Cost  of  Manufactures 8vo,  5  00 

Benjamin's  Wrinkles  and  Recipes 12mo,  2  00 

Dingey's  Machinery  Pattern  Making 12mo,  2  00 

METALLURGY. 

IRON— GOLD— SILVER — ALLOYS,  ETC. 

Egleston's  Metallurgy  of  Silver 8vo,  1  50 

Gold  and  Mercury 8vo,  750 

"  Weights  and  Measures,  Tables 18uio,  75 

Catalogue  of  Minerals 8vo,  250 

O'Driscoll's  Treatment  of  Gold  Ores 8vo,  2  00 

*  Kerl's  Metallurgy — Copper  and  Iron 8vo,  15  00 

*  "           "               Steel,  Fuel,  etc 8vo,  1500 

12 


Thurston's  Iron  and  Steel 8vo,  $3  50 

Alloys 8vo,  250 

Troilius's  Chemistry  of  Iron , Svo,  2  00 

Kimhnrdt's  Ore  Dressing  in  Europe 8vo,  1  50 

Weyrauch's  Strength  of  Iron  and  Steel.    (Du  Bois.) 8vo,  1  50 

Beardslee  and  Kent's  Strength  of  Wrought  Iron, 8vo,  1  50 

Compton's  First  Lessons  in  Metal  Working 12mo,  1  50 

West's  American  Foundry  Practice 12mo,  2  50 

"      Moulder's  Text-book 12mo,  250 


MINERALOGY  AND  MINING. 

MINE  ACCIDENTS — VENTILATION— ORE  DRESSING,  ETC. 

Dana's  Descriptive  Mineralogy.     (E.  S.) .8vo,  half  morocco,  12  50 

"      Mineralogy  and  Petrography.     (J.  D.) 12mo,  2  00 

"      Text-book  of  Mineralogy.    (E.  S.) 8vo,  350 

"      Minerals  and  How  to  Study  Them.     (E.  S.) 12mo,  1  50 

"      American  Localities  of  Minerals 8vo,  1  00 

Brush  and  Dana's  Determinative  Mineralogy 8vo,  3  50 

Rosenbuscli's    Microscopical    Physiography  of    Minerals    and 

Rocks.     (Iddings.) 8vo,  500 

Hussak's  Rock-forming  Minerals.     (Smith.) 8vo,  2  00 

Williams's  Lithology 8vo,  3  00 

Chester's  Catalogue  of  Minerals 8vo,  1  25 

"        Dictionary  of  the  Names  of  Minerals 8vo,  3  00 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Goodyear 's  Coal  Mines  of  the  Western  Coast 12mo,  2  50 

Kunhardt's  Ore  Dressing  in  Europe 8vo,  1  50 

Sawyer's  Accidents  in  Mines 8vo,  7  00 

Wilson's  Mine  Ventilation 16mo,  1  25 

Boyd's  Resources  of  South  Western  Virginia 8vo,  3  00 

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13 


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H 


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15 


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